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THE DANCING MOUSE 



THE MACMILLAN COMPANY 

NEW YOKK • BOSTON • CHICAGO 
ATLANTA • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY • CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 





Dancing Mice — Sniffing and Eating. 



THE ANIMAL BEHAVIOR SERIES. VOLUME I 



THE DANCING MOUSE 

A Study in Animal Behavior 



BY 



ROBERT M. lYERKES, Ph.D. 

INSTRUCTOR IN COMPARATIvF^SYCHOLOGY IN HARVARD 
UNIVERSITY 



The Cartwright Prize of the Alumni Association of the College of Physicians 
and Surgeons, Columbia University, was awarded, in rgoj, for an Essay 
which comprised the first twelve chapters of this volume. 



THE MACMILLAN COMPANY 
1907 

All rights reserved 



Copyright, 1907, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published October, 1907. 



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Norinootj ^i^xtw 

J. 8. Gushing Co, — Berwick & Smith Co. 

Norwood, Mass., U.S.A. 



/9c7 



IN LOVE AND GRATITUDE 

THIS BOOK IS DEDICATED TO 

MY MOTHER 



m\ 



PREFACE 

This book is the direct result of what, at the time of its 
occurrence, seemed to be an unimportant incident in the 
course of my scientific work — the presentation of a pair of 
dancing mice to the Harvard Psychological Laboratory. 
My interest in the peculiarities of behavior which the crea- 
tures exhibited, as I watched them casually from day to day, 
soon became experiment-impelling, and almost before I real- 
ized it, I was in the midst of an investigation of their senses 
and intelligence. 

The longer I observed and experimented with them, the 
more numerous became the problems which the dancers 
presented to me for solution. From a study of the senses 
of hearing and sight I was led to investigate, in turn, the 
various forms of activity of which the mice are capable ; the 
ways in which they learn to react adaptively to new or novel 
situations ; the facility with which they acquire habits ; the 
duration of habits; the roles of the various senses in the 
acquisition and performance of certain habitual acts; the 
efficiency of different methods of training ; and the inheritance 
of racial and individually acquired forms of behavior. 

In the course of my experimental work I discovered, much 
to my surprise, that, no accurate and detailed account of this 
curiously interesting animal existed in the English language, 
and that in no other language were all the facts concerning 
it available in a single book. This fact, in connection with 
my appreciation of the exceptional value of the dancer as a 
pet and as material for the scientific study of animal behavior, 
has led me to supplement the results of my own observation. 



viii Preface 

by presenting in this little book a brief and not too highly 
technical description of the general characteristics and his- 
tory of the dancer. 

The purposes which I have had in mind as I planned and 
wrote the book are three : first, to present directly, clearly, 
and briefly the results of my investigation ; second, to give 
as complete an account of the dancing mouse as a thorough 
study of the literature on the animal and long-continued 
observation on my own part should make possible ; third, to 
provide a supplementary text-book on mammalian behavior 
and on methods of studying animal behavior for use in con- 
nection with courses in Comparative Psychology, Compara- 
tive Physiology, and Animal Behavior. 

It is my conviction that the scientific study of animal be- 
havior and of animal mind can be furthered more just at 
present by intensive special investigations than by extensive 
general books. Methods of research in this field are few 
and surprisingly crude, for the majority of investigators have 
been more deeply interested in getting results than in per- 
fecting methods. In writing this account of the dancing 
mouse I have attempted to lay as much stress upon the de- 
velopment of my methods of work as upon the results which 
the methods yielded. In fact, I have used the dancer as a 
means of exhibiting a variety of methods by which the be- 
havior and intelligence of animals may be studied. As it 
happens the dancer is an ideal subject for the experimental 
study of many of the problems of animal behavior. It is 
small, easily cared for, readily tamed, harmless, incessantly 
active, and it lends itself satisfactorily to a large number of 
experimental situations. For laboratory courses in Compara- 
tive Psychology or Comparative Physiology it well might 
hold the place which the frog now holds in courses in Com- 
parative Anatomy. 



Preface ix 

Gratefully, and with this expression of my thanks, I ac- 
knowledge my indebtedness to Professor Hugo Miinsterberg 
for placing at my command the resources of the Harvard 
Psychological Laboratory and for advice and encouragement 
throughout my investigation; to Professor Edwin B. Holt 
for valuable assistance in more ways than I can mention ; 
to Professor Wallace C. Sabine for generous aid in connec- 
tion with the experiments on hearing ; to Professor Theobald 
Smith for the examination of pathological dancers ; to Miss 
Mary C. Dickerson for the photographs of dancing mice 
which are reproduced in the frontispiece; to Mr. Frank Ash- 
more for additional photographs which I have been unable 
to use in this volume ; to Mr. C. H. Toll for the drawings 
for Figures 14 and 20; to Doctors H. W. Rand and C. S. 
Berry for valuable suggestions on the basis of a critical read- 
ing of the proof sheets; and to my wife, Ada Watterson 
Yerkes, for constant aid throughout the experimental work 
and in the preparation of this volume. 

R. M. Y. 
Cambridge, Massachusetts, 
August, 1907. 



CONTENTS 

PAGE 

List of Illustrations xvii 

Literature on the Dancing Mouse xix 

CHAPTER I 

Characteristics, Origin, and History i 

Peculiarities of the dancing mouse — Markings and method 
of keeping record of individuals — The dancer in China and 
Japan (Kishi, Mitsukuri, Hatai) — Theories concerning the 
origin of the race : selectional breeding ; the inheritance of 
an acquired character ; mutation, inheritance, and selectional 
breeding ; pathological changes ; natural selection — In- 
stances of the occurrence of dancers among other kinds of 
mice — Results of crossing dancer with other kinds of mice. 

CHAPTER II 
Feeding, Breeding, and Development of the Young . i6 
Methods of keeping and caring for dancers — Cages, nest- 
boxes, and materials for nest — Cleansing cages — Food 
supply and feeding — Importance of cleanliness, warmth, and 
pure food — Relations of males and females, fighting — The 
young, number in a litter — Care of young — Course of de- 
velopment — Comparison of young of dancer with young of 
common mouse — Diary account of the course of develop- 
ment of a typical litter of dancers. 

CHAPTER III 

Behavior : Dance Movements 29 

Dancing — Restlessness and excitability — Significance of 
restlessness — Forms of dance : whirling, circling, and figure- 
eights — Direction of whirling and circling: right whirlers, 
left whirlers, and mixed whirlers — Sex differences in danc- 
ing — Time and periodicity of dancing — Influence of light 
on activity — Necessity for prolonged observation of behavior. 



xii Contettls 

CHAPTER IV 

PAGE 

Behavior: Equilibration and Dizziness .... 41 
Muscular coordination — Statements of Cyon and Zoth 
concerning behavior — Control of movements, orientation, 
equilibration, movement on inclined surfaces, climbing — 
The tracks of the dancer — Absence of visual dizziness — 
Comparison of the behavior of the dancer with that of the 
common mouse when they are rotated in a cyclostat — Be- 
havior of blinded dancers (Cyon, Alexander and Kreidl, 
Kishi) — Cyon's two types of dancer — Phenomena of be- 
havior for which structural bases are sought: dance move- 
ments ; lack of response to sounds ; deficiency in equilibrational 
ability ; lack of visual and rotational dizziness. 

CHAPTER V 
Structural Peculiarities and Behavior .... 52 
The functions of the ear — Structure of the ear of the 
dancer as described by Rawitz, by Panse, by Baginsky, by 
Alexander and Kreidl, and by Kishi — Cyon's theory of the 
relation of the semicircular canals to space perception — Con- 
dition of the auditory organs — Condition of the equilibra- 
tional organs — Condition of the sound-transmitting organs 
— The bearing of the results of anatomical investigations 
upon the facts of behavior. 

CHAPTER VI 

The Sense of Hearing 73 

Experiments on hearing in the dancer made by Rawitz, 
by Panse, by Cyon, by Alexander and Kreidl, by Zoth, and 
by Kishi — Hearing and the voice — Methods of testing sen- 
sitiveness to sounds — Results of tests with adults — Im- 
portance of indirect method of experimentation — Results of 
tests with young — The period of auditory sensitiveness — 
Individual differences. 

CHAPTER VII 
The Sense of Sight: Brightness Vision .... 91 
What is known concerning sight in the dancer — Bright- 
ness vision and color vision — Methods of testing brightness 



Contents xiii 



PAGE 

vision, the visual discrimination apparatus — Motives for 
discrimination and choice — Punishment versus reward as an 
incentive in animal experiments — Hunger as an incentive — 
An electric stimulus as an incentive — Conditions for bright- 
ness vision tests — White-black vision — Evidence of prefer- 
ence — Check experiments — Conclusion. 

CHAPTER Vni 

The Sense of Sight: Brightness Vision {Continued) . 113 
The delicacy of brightness discrimination — Methods of 
testing the dancer's ability to detect slight differences in 
brightness — Results of tests with gray papers — Relation 
of intensity of visual stimuli to the threshold of discrimina- 
tion — Weber's law apparatus and method of experimentation 

— Results of Weber's law tests — Practice effects, the train- 
ing of vision — Description of the behavior of the dancer in 
the discrimination box experiments — Modes of choice : by 
afifirmation ; by negation ; by comparison — Evidence of 
indiscriminable visual conditions. 

CHAPTER IX 

The Sense of Sight : Color Vision 133 

Does the dancer see colors? — The food-box method of 
testing color vision — Waugh's food-box method — Results 
of tests — Tests by the use of colored papers in the visual 
discrimination box — Yellow-red vision — Blue-orange vision 

— Brightness vision versus color vision — Brightness check 
tests — Green-blue vision — Violet-red vision — Conclusions. 

CHAPTER X 

The Sense of Sight: Color Vision {Continued) . .151 
The use of color filters — Testing color vision by the use 
of transmitted light — Green-blue vision — Green-red vision 

— Blue-red vision — Stimulating value of different portions 
of the spectrum — Does red appear darker to the dancer than 
to us ? — Conclusions concerning color vision — Structure of 
the retina of the dancer and its significance. 



xiv C 071 tents 

CHAPTER XI 

The Role of Sight in the Daily Life of the Dancer . 
Sight and general behavior — Behavior of blinded dancers 

— Experimental tests of ability to perceive form — Visual 
guidance in mazes — Following labyrinth paths in the dark 

— The relative importance of visual, olfactory, and kinaesthetic 
stimuli — Conditions for the acquisition of a motor habit — 
Conditions for the execution of an habitual act. 

CHAPTER Xn 

Educability: Methods of Learning 

The modifiability of behavior — Educational value of ex- 
perimental studies of modifiability — Methods: the problem 
method; the labyrinth method; the discrimination method 

— Relation of method to characteristics of animal — Simple 
test of the docility of the dancer — Lack of imitative tendency 

— Persistence of useless acts — Manner of profiting by expe- 
rience — Individual differences in initiative. 

CHAPTER XIII 

Habit Formation: The Labyrinth Habit . . . . 

The labyrinth method — Problems — Preliminary tests — 

Comparison of the behavior of the dancer in a maze with 

that of the common mouse — Evolution of a labyrinth method 

— Records of time and records of errors — Simple and effec- 
tive method of recording the path — Curves of habit formation 

— Regular and irregular labyrinths — Points for a standard 
labyrinth — Values and defects of the labyrinth method. 

CHAPTER XIV 

Habit Formation: The Discrimination Method 

Quantitative versus qualitative results — Motives — Pre- 
cautions — Preference — Results of systematic habit-forming 
experiments — Curves of habit formation — Meaning of ir- 
regularity in curve — Individual differences — Comparison of 
curves for discrimination habits with those for labyrinth 
habits — Averages — The index of modifiability as a measure 
of docility — Reliability of the index. 



Contents xv 



CHAPTER XV 



PAGE 



The Efficiency of Training Methods .... 239 
Importance of measuring the efficiency of educational 
methods — Rapidity of learning and permanency of modifica- 
tions wrought by training — Results of a study of the efficiency 
of discrimination methods — Comparison by means of indices 
of modifiability — Number of tests per series versus number of 
series — Efficiency as measured by memory tests. 

CHAPTER XVI 

The Duration of Habits: Memory and Re-learning . 251 
Measures of the permanency of modifications in behavior 

— The duration of brightness and color discrimination habits 

— The relation of learning to re-learning — Can a habit which 
has been lost completely be re-acquired with greater facility 
than it was originally acquired? — Relation of special train- 
ing to general efficiency — Does the training in one form of 
labyrinth aid the dancer in acquiring other labyrinth habits? 

CHAPTER XVII 

Individual, Age, and Sex Differences in Behavior . . 264 
Individual peculiarities in sensitiveness, docility, and initia- 
tive — The relation of docility to age — The individual result 
and the average — How averages conceal facts — Sex differ- 
ences in docility and initiative — Individual differences of 
motor capacity which seem to indicate varieties — Is the 
dancer pathological ? 

CHAPTER XVIII 

The Inheritance of Forms of Behavior .... 278 
Characteristics of the race — Inheritance of the tendency 
to whirl in a particular way — Tests of the inheritance of 
individually acquired forms of behavior. 

Index 285 



ILLUSTRATIONS 



Dancing Mice — sniffing and eating .... Frontispiece 

FIGURE PAGB 

1. Color patterns of dancers. Record blanks .... 4 

2. Double cage, with nest-boxes and water dishes . . • 17 

3. Double cages in frame .18 

4. Photographs of dancers climbing (After Zoth) ... 43 

5. Tracks of common mouse (After Alexander and Kreidl) . 44 

6. Tracks of dancer (After Alexander and Kreidl) ... 44 

7. The inner ear of the rabbit (Retzius) 54 

8. The membranous labyrinth of the ear of the dancer (After 

Rawitz) 56 

9. Same 57 

10. Same ........... 57 

11. Model of the ear of the dancer (After Baginsky) ... 58 

12. Ear of the dancer (After Kishi) ...... 66 

13. Ear of the dancer (After Kishi) 67 

14. Discrimination box 92 

1 5 . Ground plan of discrimination box ..... 93 

16. Nendel's gray papers 115 

17. Weber's law apparatus 119 

18. Food-box apparatus . . . . . . . .134 

19. Waugh's food-box apparatus . . . , . '135 

20. Color discrimination apparatus 153 

21. Ground plan of color discrimination apparatus . . .154 

22. Cards for form discrimination 182 

23. Labyrinth B • . . . 184 

24. Labyrinth B on electric wires . . . . . .188 

25. Labyrinth A 211 

26. Curves of habit formation for labyrinth B . . . .217 

27. Plan of labyrinth C, and path records . . . . .219 

28. Labyrinth D 222 

29. Curve of learning for white-black discrimination, twenty 

individuals 231 

xvii 



xviii Illustrations 

FIGURE PAGE 

30. Curve of learning for white-black discrimination, thirty 

individuals 233 

31. Curve of habit formation for labyrinth D .... 235 

32. Curves of learning and re-learning 257 

33. Plasticity curves . . . . . . . , . 273 



LITERATURE ON THE DANCING 
MOUSE 

1. Alexander, G. und Kreidl, A. "Zur Physiologie des Laby- 

rinths der Tanzmaus." Archiv fur die gesammte Physiologie, 
Bd. 82: 541-552. 1900. 

2. Alexander, G. und Kreidl, A. " Anatomisch-physiologische 

Studien uber das Ohriabyrinth der Tanzmaus." II Mittheilung. 
Archiv fUr die gesafnmte Physiologie, 'Qd. %^ : 509-563. 1902. 

3. Alexander, G. und Kreidl, A. "Anatomisch-physiologische 

Studien iiber das Ohriabyrinth der Tanzmaus." Ill Mitthei- 
lung. Archiv fur die gesammte Physiologie, Bd. 88: 564-574. 
1902. 

4. Baginsky, B. "Zur Frage iiber die Zahl der Bogengange bei 

japanischen Tanzmausen. Centralblatt fur Physiologie, Bd. 1 6 : 
2-4. 1902. 

5. Bateson, W. " The present state of knowledge of colour-heredity 

in mice and rats." Proceedings of the Zoological Society of Lon- 
don,Wo\.2: 71-99. 1903. 

6. Brehm, A. E. "Tierleben." Dritte Auflage. Saugetiere^ Bd. 2 : 

513-514. 1890. 

7. Brehm, A. E. " Life of Animals." Translated from the third 

German edition of the "Tierleben" by G. R. Schmidtlein. 
Mammalia, p. 338. Marquis, Chicago. 1895. 

8. Cyon, E. de. " Le sens de Tespace chez les souris dansantes 

japonaises." Cinquantettaire de la Sociiti de Biologie (Volume 
jubilaire). p. 544-546. Paris. 1899. 

9. Cyon, E. von. "Ohriabyrinth, Raumsinn und Orientirung." 

Archiv fur die gesammte Physiologie, Bd. 79 : 211-302. 1900. 

10. Cyon, E. de. "Presentation de souris dansantes japonaises." 
Comptes rendus du XJII Congres International de Paris, Section 
de physiologie, p. 1 60-1 61. 1900. 



XX Literature on the Dancing Mouse 

11. Cyon, E. von. "Beitrage zur Physiologic des Raumsinns." I 

Theil. " Neue Beobachtungen an den japanischen Tanzmau- 

sen." Archiv /lir die gesamnite FhystologieyBd.2><^: 427-453. 
1902. 

12. Cyon, E. DE. « Le sens de Tespace." Richef s " Dictionnaire de 

physiologie," T. 5 : 570-571. 1901. 

13. Darbishire, a. D. Note on the results of crossing Japanese 

waltzing mice with European albino races. Biometrica, Vol. 2 : 
101-104. 1902. 

14. Darbishire, A. D. Second report on the result of crossing 

Japanese waltzing mice with European albino races. Biotnet- 
rtca,Yo\. 2: 165-173. 1903. 

15. Darbishire, A. D. Third report on hybrids between waltzing 

mice and albino races. Biometrica, Vol. 2 : 282-285. 1903. 

16. Darbishire, A. D. On the result of crossing Japanese waltzing 

with albino mice. Biometrica^YoX. '^•. 1-5 1. 1904. 

17. GuAiTA, G. V. "Versuche mit Kreuzungen von verschiedenen 

Rassen der Hausmaus." Berichte der naturforschenden Gesell- 
schaft zu Freiburg /. ^., Bd. 10 : 317-332. 1898. 

18. GuAlTA, G. V. "Zweite Mitteilung iiber Versuche mit Kreuzun- 

gen von verschiedenen Hausmausrassen." Berichte der natur- 
forschenden Gesellschaft zu Freiburg i. B.j Bd. 11 : 131-138. 
1900. 

19. Haacke, W. "Ueber Wesen, Ursachen und Vererbung von 

Albinismus und Scheckung und iiber deren Bedeutung fiir 
vererbungstheoretische und entwicklungsmechanische Fragen." 
Biologisches Centralblatt, Bd. 15: 44-78. 1895. 

19a. Hunter, M. S. "A Pair of Waltzing Mice." The Century 
Magazine^ Vol. 73: 889-893. April, 1907. 

20. Kammerer, p. " Tanzende Waldmaus und radschlagende Haus- 

maus." Zoologische Garten, Bd. 41 : 389-390. 1900. 

21. KiSHi, K. "Das Gehororgan der sogenanntenTanzmaus." Zeit- 

schrift fur wissenschaftliche Zoologie, Bd. 71 : 457-485. 1902. 

22. Landois, H. "Chinesische Tanzmause." Jahresbericht des 

Westfdlischen Provinzial-Vereins, Miinster, 1 893-1 894: 62-64. 

22a. Lose, J. "Waltzing Mice." Country Life in America, Sep- 
tember, 1904. p. 447. 



Literature on the Dancing Mouse xxi 

23. Panse, R. Zu Herrn Bernhard Rawitz' Arbeit : " Das Gehororgan 

der japanischen Tanzmause." Archiv fur Anatomie und Physi- 
ologie, Physiologische Abtheilung, 1901 : 139-140. 

24. Panse, R. *'Das Gleichgewichts- und Gehororgan der japan- 

ischen Tanzmause." Munchener inedicinische Wochenschrift^ 
Jahrgang 48, Bd. i: 498-499. 1901. 

25. Rawitz, B. "Das Gehororgan der japanischen Tanzmause." 

Archiv fur Anatomie und Physiologie, Physiologische Abthei- 
lung, 1899: 236-243. 

26. Rawitz, B. " Neue Beobachtungen iiber das Gehororgan japan- 

ischer Tanzmause." Archiv fur Anatomie und Physiologie^ 
Physiologische Abtheilung, 1901, Supplement: 171-176. 

27. Rawitz, B. "Zur Frage uber die Zahl der Bogengange bei japan- 

ischen Tanzmausen." Centralblatt fur Physiologic^ Bd. 15: 
649-651. 1902. 

28. Saint-Loup, R. " Sur le movement de manege chez les souris." 

Bulletin de la Societt Zoologique de France, T. 18: 85-88. 
1893. 

29. SCHLUMBERGER, C. "A propos d\m netzuke japonais." Me- 

moir es de la Sociite Zoologique de France, T. 7 : 63-64. 1894. 

30. Weldon, W. F. R. Mr. Bateson's revisions of Mendel's theory 

of heredity. Biometrica,Yo\. 2: 286-298. 1903. 

31. ZOTH, O. " Ein Beitrag zu den Beobachtungen und Versuchen 

an japanischen Tanzmausen." Archiv fur die gesammte Physi- 
ologic, ^di, ^d: 147-176. 1901. 

32. Anonymous. "Fancy Mice: Their Varieties, Management, and 

Breeding." Fourth edition. London : L. Upcott Gill. No 
date. 



THE DANCING MOUSE 

CHAPTER I 
Characteristics, Origin, and History 

The variety of mouse which is known as the Japanese 
dancing or waltzing mouse has been of special interest to 
biologists and to lovers of pets because of its curious move- 
ments. Haacke in Brehm's "Life of Animals" (7 p. 337) ^ 
writes as follows concerning certain mice which were brought 
to Europe from China and Japan: "From time to time a 
Hamburg dealer in animals sends me two breeds of common 
mice, which he calls Chinese climbing mice (Chinesische 
Klettermause) and Japanese dancing mice (Japanische 
Tanzmause). It is true that the first are distinguished only 
by their different colors, for their climbing accomplishments 
are not greater than those of other mice. The color, how- 
ever, is subject to many variations. Besides individuals 
of uniform gray, light yellow, and white color, I have had 
specimens mottled with gray and white, and blue and white. 
Tricolored mice seem to be very rare. It is a known fact that 
we also have white, black, and yellow mice and occasionally 
pied ories, and the Chinese have profited by these variations 
of the common mouse also, to satisfy their fancy in breeding 
animals. The Japanese, however, who are no less enthu- 
siastic on this point, know how to transform the common 

^ The reference numbers, of which 7 is an example, refer to the numbers 
in the bibliographic list which precedes this chapter. 
B I 



2 The Dancing Mouse 

mouse into a really admirable animal. The Japanese 
dancing mice, which perfectly justify their appellation, also 
occur in all the described colors. But what distinguishes 
them most is their innate habit of running around, describing 
greater or smaller circles or more frequently whirling around 
on the same spot with incredible rapidity. Sometimes two 
or, more rarely, three mice join in such a dance, which usually 
begins at dusk and is at intervals resumed during the night, 
but it is usually executed by a single individual." 

As a rule the dancing mouse is considerably smaller than 
the common mouse, and observers agree that there are also 
certain characteristic peculiarities in the shape of the head. 
One of the earliest accounts of the animal which I have found, 
that of Landois (22 p. 62), states, however, that the peculiari- 
ties of external form are not remarkable. Landois further 
remarks, with reason, that the name dancing mouse is ill 
chosen, since the human dance movement is rather a rhyth- 
mic hopping motion than regular movement in a circle. As 
he suggests, they might more appropriately be called "circus 
course mice" (22 p. 63). 

Since 1903 I have had under observation constantly from 
two to one hundred dancing mice. The ori^nal pair was 
presented to the Harvard Psychological Laboratory by 
Doctor A. G. Cleghorn of Cambridge. I have obtained speci- 
mens, all strikingly alike in markings, size, and general 
behavior, from animal dealers in Washington, Philadelphia, 
and Boston. Almost all of the dancers which I have had, 
and they now number about four hundred, were wKite with 
patches, streaks, or spots of black. The black markings 
occurred most frequently on the neck, ears, face, thighs, hind 
legs, about the root of the tail, and occasionally on the tail 
itself. In only one instance were the ears white, and that in 
the case of one of the offspring of a male w^hich was distin- 



Characteristics, Origin, and History 3 

guished from most of his fellows by the possession of one 
white ear. I have had a few individuals whose markings 
were white and gray instead of white and black. 

The method by which I was able to keep an accurate 
record of each of my dancers for purposes of identification and 
reference is illustrated in Figure i. As this method has 
proved very convenient and satisfactory, I may briefly de- 
scribe it. With a rubber stamp ^ a rough outline of a mouse, 
like that of Figure i A, was made in my record book. 
On this outline I then indicated the black markings of the 
individual to be described. Beside this drawing of the ani- 
mal I recorded its number, sex,^ date of birth, parentage, 
and history. B, C, and D of Figure i represent typical 
color patterns. D indicates the markings of an individual 
whose ears were almost entirely white. The pattern varies 
so much from individual to individual that I have had no 
trouble whatever in identifying my mice by means of such 
records as these. 

All of my dancers had black eyes and were smaller as 
well as weaker than the albino mouse and the gray house 
mouse. The weakness indicated by their inability to hold 
up their own weight or to cling to an object curiously enough 
does not manifest itself in their dancing; in this they are 
indefatigable. Frequently they run in circles or whirl about 
with astonishing rapidity for several minutes at a time. 
Zoth (31 p. 173), who measured the strength of the dancer 

* For the use of the plate from which this stamp was made, I am in- 
debted to Professor W. E. Castle, who in turn makes acknowledgment to 
Doctor G. M. Allen for the original drawing. 

^ I have found it convenient to use the even numbers for the males and 
the odd numbers for the females. Throughout this book this usage is 
followed. Wherever the sex of an individual is not specially given, the 
reader therefore may infer that it is a male if the number is even ; a female 
if the number is odd. 



The Dancing Mouse 



in comparison with that of the common mouse, found that 
it can hold up only about 2.8 times its own weight, whereas 
the common white mouse can hold up 4.4 times its weight. 







Figure i. — Typical markings of dancers. -4, blank outline of mouse for record. 
B, markings of No. 2 cT, born September 7, 1905, of unknown parents, died 
March 30, 1907. C, markings of No. 43 9, born November 10, 1906, of 212 and 
211. D, markings of No. 151 ?, born February 28, 1906, of 1000 and 5, died 
Febniary 26, 1907. 



Characteristics^ Origin^ and History 5 

No other accurate measurements of the strength, endurance, 
or hardiness of the dancer are available. They are usually 
supposed to be weak and delicate, but my own observations 
cause me to regard them as exceptionally strong in certain 
respects and weak in others. 

What the Japanese have to say about the dancing mouse 
is of special importance because Japan is rather commonly 
supposed to be its home. For this reason, as well as because 
of the peculiar interest of the facts mentioned, I quote at 
length from Doctor Kishi (21 p. 457). " The dancing mouse 
has received in Europe this name which it does not bear in 
its own home, because of the fact that the circular move- 
ments which it makes are similar to the European (human) 
dance. Sometimes it is also called the Japanese or Chinese 
mouse ; originally, however, China must have been its home, 
since in Japan it is mostly called ''Nankin nesumi,^ the mouse 
from Nankin. When this animal came from China to Japan 
I shall inquire at a later opportunity. There were origi- 
nally in Japan two different species of mouse, the gray and 
the white; therefore in order to distinguish our daj^ing 
mouse from these it was necessary to use the name of its 
native city. 

"In Japan, as in Europe, the animal lives as a house 
animal in small cages, but the interest which is taken in it 
there is shown in quite another way than in Europe, where 
the whirling movements, to which the name dancing mouse 
is due, are of chief interest. For this reason in Europe it is 
given as much room as possible in its cage that it may dance 
conveniently. In Japan also the circular movements have 
been known for a long time, but this has had no influence 
upon our interest in the animal, for the human fashion of 
dancing with us is quite different from that in Europe. What 
has lent interest to the creature for us are its prettiness, its 



6 The Dancing Mouse 

cleverness in tricks, and its activity. It is liked, therefore, 
as an amusement for children. For this purpose it is kept 
in a small cage, usually fifteen centimeters square, sometimes 
in a somewhat broader wooden box one of whose walls is of 
wire netting. In this box are built usually a tower, a tunnel, 
a bridge, and a wheel. The wheel is rather broad, being 
made in the form of a drum and pierced with holes on one 
side through which the animal can slip in and out. Run- 
ning around on the inside, the mouse moves the wheel often 
for hours at a time, especially in the evening. Moreover, 
there are found in the box other arrangements of different 
kinds which may be set in motion by the turning of the 
wheel. No space remains in the box in which the animal 
may move about freely, and therefore one does not easily or 
often have an opportunity to observe that the animal makes 
circular movements, whether voluntarily or involuntarily. 
This is the reason that in its home this interesting httle 
animal has never been studied by any one in this respect." 

It is odd indeed that the remarkable capacity of the dancer 
for the execution of quick, graceful, dextrous, bizarre, and 
oft-repeated movements has not been utilized in America as 
it has in Japan. The mice are inexhaustible sources of 
amusement as well as invaluable material for studies in 
animal behavior and intelligence. 

Concerning the origin and history of this curious variety 
of mouse little is definitely known. I have found no men- 
tion of the animal in scientific literature previous to 1890. 
The fact that it is called the Chinese dancing mouse, the 
Japanese dancing mouse, and the Japanese waltzing mouse 
is indicative of the existing uncertainty concerning the origin 
of the race. 

Thinking that Japanese literature might furnish more in- 
formation bearing on the question of racial history than was 



Characteristics, Origin, and History 7 

available from European sources, I wrote to Professor 
Mitsukuri of the University of Tokyo, asking him whether 
any reliable records of the dancer existed in Japan. He 
replied as follows: "I have tried to find what is known in 
Japan about the history of the Japanese waltzing mice, but 
I am sorry to say that the results are wholly negative. I 
cannot find any account of the origin of this freak, either 
authentic or fictitious, and, strange as it may seem to you, 
no study of the mice in a modern sense has been made, so 
you may consider the literature on the mouse in the Japanese 
language as absolutely nilP In explanation of this some- 
what surprising ignorance of the origin of the race in what 
is commonly supposed to be its native land. Professor Mit- 
sukuri adds: "The breeders of the mice have mostly been 
ignorant men to whom writing is anything but easy." 

In response to similar inquiries, I received the following 
letter, confirmatory of Professor Mitsukuri's statements, from 
Doctor S. Hatai of Wistar Institute, Philadelphia: "If I 
remember rightly the so-called Japanese dancing mouse is 
usually called by us N ankin-nedzumi {Nankin means any- 
thing which has been imported from China, and nedzumi 
means rat-Hke animal, or in this case mouse) or Chinese 
mouse. I referred to one of the standard Japanese diction- 
aries and found ttfe following statement: 'The N ankin- 
nedzumi is one of the varieties of Mus spiciosus {Hatszuka- 
nedzumi), and is variously colored. It was imported from 
China. These mice are kept in cages for the amusement of 
children, who watch their play.' Mus spiciosus, if I remem- 
ber correctly, is very much like Mus musculus in color, size, 
and several other characteristics, if not the same altogether." 

In Swinhoe's list of the mammals of China, which appeared 
in the Proceedings of the Zoological Society oj London for 
1870, Mus musculus L. is mentioned as occurring in houses 



8; The Dancing Mouse 

in South China and in Formosa. It is further stated that 
black and white varieties which are brought from the Straits 
are often kept by the Chinese (p. 637). 

The statements of Kishi, Mitsukuri, and Hatai which have 
been quoted, taken in connection with the opinions expressed 
by various European scientists who have studied the dancer, 
make it seem highly probable that the race appeared first in 
China, and was thence introduced into Japan, from which 
country it has been brought to Europe and America. Accept- 
ing for the present this conclusion with reference to the place 
of origin of the dancer, we may now inquire, how and when 
did this curious freak, as Professor Mitsukuri has called it, 
come into existence? Concerning these matters there is 
wide divergence of opinion. 

Haacke (6 p. 514), as quoted in Brehm's "Tierleben," says 
that an animal dealer with whom he discussed the question 
of the possible origin of the dancer maintained that it came 
from Peru, where it nests in the full cotton capsules, arrang- 
ing the cotton fibers in the form of a nest by running about 
among them in small circles. Hence the name cotton mouse 
is sometimes applied to it. Haacke himself believes, how- 
ever, that the race originated either in China or japan as 
the result of systematic selectional breeding. Of this he has 
no certainty, for he states that he failed to find any literature 
on the "beautiful mice of China and Japan." Whether 
Haacke' s description of the dancing mouse was pubHshed 
elsewhere previous to its appearance in Brehm's ''Tierleben" 
I am unable to state ; I have found nothing written on the 
subject by him before 1890. Zoth (31 p. 176) also thinks 
that the race was developed by systematic breeding, or in other 
words, that it is a product of the skill of the Asiatic animal 
breeders. 

Another account of the origin of the race is that accepted 



Characteristics^ Origin, and History 9 

by Kishi (21 p. 481) and some other Japanese biologists. It 
is their behef that the forms of movement acquired by the 
individual as the result of confinement in narrow cages are 
inherited. Thus centuries of subjection to the conditions 
which Kishi has described (p. 6) finally resulted in a race of 
mice which breed true to the dance movement. It is only 
fair to add, although Kishi does not emphasize the fact, that 
in all probability those individuals in which the dancing 
tendency was most pronounced would naturally be selected 
by the breeders who kept these animals as pets, and thus 
it would come about that selectional breeding would supple- 
ment the inheritance of an acquired character. Few indeed 
will be willing to accept this explanation of the origin of the 
dancer so long as the inheritance of acquired characters 
remains, as at present, unproved. 

Still another mode of origin of the mice is suggested by 
the following facts. In 1893 Saint Loup (28 p. 85) advanced 
the opinion that dancing individuals appear from time to 
time among races of common mice. The peculiarity of 
movement may be due, he thinks, to an accidental nervous 
defect which possibly might be transmissible to the offspring 
of the exceptional individual. Saint Loup for several months 
had under observation a litter of common mice whose quick, 
jerky, nervous movements of the head, continuous activity, 
and rapid whirling closely resembled the characteristic move- 
ments of the true dancers of China. He states that these 
mice ran around in circles of from i to 20 cm. in diameter. 
They turned in either direction, but more frequently to the 
left, that is, anticlockwise. At intervals they ran in figure- 
eights (00 ) as do the true dancers. According to Saint Loup 
these exceptional individuals were healthy, active, tame, and 
not markedly different in general intelligence from the or- 
dinary mouse. One of these mice produced a litter of seven 



lo The Dancing Mouse 

young, in which, however, none of the peculiarities of 
behavior of the parents appeared. 

In view of this proof of the occurrence of dancing indi- 
viduals among common mice, Saint Loup believes that the 
race of dancers has resulted from the inheritance and ac- 
centuation of an "accidental" deviation from the usual mode 
of behavior. It is scarcely necessary to say that this opinion 
would be of far greater weight had he observed, instead of 
postulating, the inheritance of the peculiarities of movement 
which he has described. It might be objected, to the first of 
his so-called facts, that the litter resulted from the mating 
of mice which possessed dancer blood. Until the occurrence 
of dancers among varieties of mice which are known to be 
unmixed with true dancers is established, and further, until 
the inheritance of this peculiar deviation from the normal 
is proved, Saint Loup's account of the origin of the dancing 
mouse race must be regarded as an hypothesis. 

The occurrence of dancing individuals among common mice 
has been recorded by several other observers. Kammerer 
(20 p. 389) reports that he found a litter of young wood 
mice {Mus sylvaticus L.) which behaved much as do the 
spotted dancers of China. He also observed, among a lot 
of true dancers, a gray individual which, instead of spinning 
around after the manner of the race, turned somersaults at 
frequent intervals. It is Kammerer's opinion, as a result 
of these observations, that the black and white dancers of 
China and Japan have been produced by selectional breed- 
ing on the basis of this occasional tendency to move in circles. 
Among albino mice Rawitz (25 p. 238) has found individuals 
which whirled about rapidly in small circles. He states, 
however, that they lacked the restlessness of the Chinese 
dancers. Some shrews {Sorex vulgaris L.) which exhibited 
whirling movements and in certain other respects resembled 



Characteristics, Origin, and History 1 1 

the dancing mouse were studied for a time by Professor 
Hacker of Freiburg in Baden, according to a report by von 
Guaita (17 p. 317, footnote). Doctor G. M. Allen of Cam- 
bridge has reported to me that he noticed among a large 
number of mice kept by him for the investigation of problems 
of heredity ^ individuals which ran in circles ; and Miss 
Abbie Lathrop of Granby, Massachusetts, who has raised 
thousands of mice for the market, has written me of the ap- 
pearance of an individual, in a race which she feels confident 
possessed no dancer blood, which whirled and ran about in 
small circles much as do the true dancers. 

Although it is possible that some of these cases of the 
unexpected appearance of individuals with certain of the 
dancer's peculiarities of behavior may have been due to 
the presence of dancer blood in the parents, it is not at 
all probable that this is true of all of them. We may, there- 
fore, accept the statement that dancing individuals now and 
then appear in various races of mice. They are usually 
spoken of as freaks, and, because of their inability to thrive 
under the conditions of life of the race in which they happen 
to appear, they soon perish. 

Another and a strikingly different notion of the origin of 
the race of dancers from those already mentioned is that of 
Cyon (11 p. 443) who argues that it is not a natural variety 
of mouse, as one might at first suppose it to be, but instead 
a pathological variation. The pathological nature of the 
animals is indicated, he points out, by the exceptionally high 
degree of variability of certain portions of the body. Ac- 
cording to this view the dancing is due to certain pathological 
structural conditions which are inherited. Cyon's belief 
raises the interesting question, are the mice normal or ab- 

» Allen, G. M. "The Heredity of Coat Color in Mice." Proc. Amer. 
Academy, Vol. 40, 59-163, 1904. 



12 The Dancing Mouse 

normal, healthy or pathological ? That the question cannot 
be answered with certainty off-hand will be apparent after 
we have considered the facts of structure and function which 
this volume presents. 

Everything organic sooner or later is accounted for, in 
some one's mind, by the action of natural selection. The 
dancing mouse is no exception, for Landois (22 p. 62) thinks 
that it is the product of natural selection and heredity, 
favored, possibly, by selectional breeding in China. He 
further maintains that the Chinese dancer is a variety of 
Mus musculus L. in which certain pecuharities of behavior 
appear because of bilateral defects in the brain. This author 
is not alone in his belief that the brain of the dancer is de- 
fective, but so far as I have been able to discover he is the 
only scientist who has had the temerity to appeal to natural 
selection as an explanation of the origin of the race. 

Milne-Edwards, as quoted by Schlumberger (29 p. 63), is 
of the opinion that the Chinese dancer is not a natural wild 
mouse race, but instead the product of rigid artificial selec- 
tion. And in connection with this statement Schlumberger 
describes a discovery of his own which seems to have some 
bearing upon the problem of origin. In an old Japanese 
wood carving which came into his possession he found a 
group of dancing mice. The artist had represented in minute 
detail the characteristics of the members of the group, which 
consisted of the parents and eight young. The father and 
mother as well as four of the little mice are represented as 
white spotted with black. Of the four remaining young mice, 
two are entirely black and two entirely white. The two pure 
white individuals have pink eyes, as has also the mother. 
The eyes of all the others are black. From these facts 
Schlumberger infers that the dancer has resulted from the 
crossing of a race of black mice with a race of albinos ; the 



Characteristics, Origin, a^id History 13 

two original types appear among the offspring in the 
carving. 

Experimental studies of the inheritance of the tendency to 
dance are of interest in their bearing upon the question of 
origin. Such studies have been made by Haacke (19), von 
Guaita (17, 18), and Darbishire (13, 14, 15, 16), and the 
important results of their investigations have been well sum- 
marized by Bateson (5). 

By crossing dancing mice with common white mice both 
Haacke and von Guaita obtained gray or black mice which 
are very similar to the wild house mouse in general appear- 
ance and behavior. The characteristic movements of the 
dancers do not appear. As the result of a long series of 
breeding experiments, Darbishire (16 pp. 26, 27) says : "When 
the race of waltzing mice is crossed with albino mice which 
do not waltz, the waltzing habit disappears in the resulting 
young, so that waltzing is completely recessive in Mendel's 
sense; the eye-color of the hybrids is always dark; the 
coat- color is variable, generally a mixture of wild-gray 
and white, the character of the coat being distinctly corre- 
lated with characters transmitted both by the albino and 
by the colored parent." When hybrids produced by the cross 
described by Darbishire are paired, they produce dancers in 
the proportion of about one to five. 

Bateson (5 p. 93, footnote), in discussing the results ob- 
tained by Haacke, von Guaita, and Darbishire, writes: ''As 
regards the waltzing character, von Guaita's experiments 
agree with Darbishire's in showing that it was always reces- 
sive to the normal. No individual in Fj [thus the first hybrid 
generation is designated] or in families produced by crossing 
Fi with the pure normal, waltzed. In Darbishire's experi- 
ments Fj X Fj [first hybrids mated] gave 8 waltzers in 37 off- 
spring, indicating i in 4 as the probable average. From von 



14 The Dancing Mouse 

Guaita's matings in the form DR x DR the totals of families 
were 117 normal and 2 1 waltzers. . . . There is therefore a 
large excess of normals over the expected 3 to i. This is 
possibly due to the delicacy of the waltzers, which are cer- 
tainly much more difficult to rear than normals are. The 
small number in von Guaita's litters makes it very likely 
that many were lost before such a character as this could be 
determined." 

Bateson does not hazard a guess at the origin of the dancer, 
but merely remarks (5 p. 86) that the exact physiological 
basis of the dancing character is uncertain and the origin of 
this curious variation in behavior still more obscure. "Mouse 
fanciers have assured me," he continues, "that something like 
it may appear in strains inbred from the normal type, though 
I cannot find an indubitable case. Such an occurrence may 
be nothing but the appearance of a rare recessive form. 
Certainly it is not a necessary consequence of inbreeding, 
witness von Guaita's long series of inbred albinos." (von 
Guaita (17 p. 319) inbred for twenty-eight generations.) 

From the foregoing survey of the available sources of in- 
formation concerning the origin and history of the race of 
dancing mice the following important facts appear. Therp 
are four theories of the origin of the race: (i) origin by selec- 
tional breeding (Haacke, Zoth, Milne-Edwards) ; (2) origin 
through the inheritance of an acquired character (Kishi); 
(3) origin by mutation, inheritance, and selectional breeding 
(Saint Loup, Kammerer, Cyon) ; (4) origin by natural selec- 
tion, and inheritance, favored by selectional breeding (Landois). 
Everything indicates that the race originated in China. It is 
fairly certain that individuals with a tendency to move in 
circles appear at rare intervals in races of common mice. 

It seems highly probable, in view of these facts, that the 
Chinese took advantage of a deviation from the usual form 



Characteristics, Origin, and History 15 

of behavior to develop by means of careful and patient selec- 
tional breeding a race of mice which is remarkable for its 
dancing. Even if it should be proved that the mutation as 
it appears among common mice is not inherited, the view 
that slight deviations were taken advantage of by the breeders 
would still be tenable. The dancing tendency is such in 
nature as to unfit an individual for the usual conditions of 
mouse existence, hence, in all probability human care alone 
could have produced and preserved the race of dancers. 

In answer to the question, how and when did the race of 
dancers originate, it may be said that historical research 
indicates that a structural variation or mutation which occa- 
sionally appears in Mus musculus, and causes those peculiari- 
ties of movement which are known as dancing, has been 
preserved and accentuated through selectional breeding by the 
Chinese and Japanese, until finally a distinct race of mice 
which breeds true to the dance character has been established. 
The age of the race is not definitely known, but it is supposed 
to have existed for several centuries. 



CHAPTER II 
Feeding, Breeding, and Development of the Young 

In this chapter I shall report, for the benefit of those who 
may wish to know how to take care of dancing mice, my 
experience in keeping and breeding the animals, and my 
observations concerning the development of the young. It 
is commonly stated that the dancer is extremely delicate, 
subject to diseases to an unusual degree and difficult to 
breed. I have not found this to be true. At first I failed to 
get them to breed, but this was due, as I discovered later, to 
the lack of proper food. For three years my mice have bred 
frequently and reared almost all of their young. During one 
year, after I had learned how to care for the animals, when 
the maximum number under observation at any time was 
fifty and the total number for the year about one hundred, I 
lost two by disease and one by an accident. I very much 
doubt whether I could have done better with any species of 
mouse. There can be no doubt, however, that the dancer 
is delicate and demands more careful attention than do 
most mice. In March, 1907, I lost almost all of my dancers 
from what appeared to be an intestinal trouble, but with this 
exception I have had remarkably good luck in breeding and 
rearing them. 

My dancers usually were kept in the type of cage of which 
Figure 2 is a photograph.^ Four of these double cages, 

* This cage was devised by Professors W. E. Castle and E. L. Mark, and 
has been used in the Zoological Laboratories of Harvard University for several 
years. • , 

16 



Feeding, Breeding, and Development 17 

70 cm. long, 45 cm. wide, and 10 cm. deep in front, were 
supported by a frame as is shown in Figure 3. The fact that 
the covers of these cages cannot be left open is of practical 
importance. A similar type of cage, which I have used to 
some extent, consists of a wooden box 30 by 30 cm. by 15 
cm. deep, without any bottom, and with a hinged cover made 




Figure 2. — Double cage, with nest boxes and water dishes. 

in part of i cm. mesh wire netting. Such a cage may be 
placed upon a piece of tin or board, or simply on a news- 
paper spread out on a table. The advantage of the loose 
bottom is that the box may be lifted off at any time, and the 
bottom thoroughly cleansed. I have had this type of cage 
constructed in blocks of four so that a single bottom and 
cover sufficed for the block. If the mice are being kept for 
show or for the observation of their movements, at least one 
side of the cages should be of wire netting, and, as Kishi 
suggests, such objects as a wheel, a tower, a tunnel, a bridge, 
and a turntable, if placed in the cage, will give the animals 
excellent opportunity to exhibit their capacity for varied 
forms of activity. 



i8 



The Dancing Mouse 



The floors of the cages were covered with a thin layer of 
sawdust for the sake of cleanliness, and in one corner of each 
cage a nest box of some sort was placed. During the warm 
months I found it convenient and satisfactory to use berry 

boxes, such as appear in 
Figure 2, with a small en- 
trance hole cut in one 
side ; and during the cold 
months cigar boxes, with 
an entrance hole not more 
than 5 cm. in diameter at 
one end. In the nest box 
a quantity of tissue paper, 
torn into fragments, fur- 
nished material for a nest 
in which the adults could 
make themselves comfort- 
able or the female care 
for her young. Cotton 
should never be used in 
the nest box6s, for the 
mice are likely to get it 

Figure 3.-Double cages in frame. wOUnd about their legs 

with serious results. Apparently they are quite unable to 
free themselves from such an incumbrance, and their spin- 
ning motion soon winds the threads so tightly that the 
circulation of the blood is stopped. 

The cages and nest boxes were emptied and thoroughly 
cleaned once a week with an emulsion made by heating to- 
gether one part of kerosene and one part of water containing 
a Httle soap. This served to destroy whatever odor the cages 
had acquired and to prevent vermin from infesting the nests. 
In hot weather far greater cleanliness is necessary for the 




Feedings Breedings and Development 19 

welfare of the mice than in cold weather. The animals 
attend faithfully to their own toilets, and usually keep them- 
selves scrupulously clean. 

For water and food dishes I have used heavy watch glasses* 
5 cm. in diameter and \ cm. deep. They are convenient 
because they are durable, easily cleaned, and not large enough 
for the young mice to drown in when they happen to spin into 
one which contains water. It is said that mice do not need 
water, but as the dancers seem very fond of a little, I have 
made it a rule to wash the watch glasses thoroughly and 
fill them with pure fresh water daily. The food, when 
moist, may be placed in the cages in the same kind of watch 
glass. 

There is no need of feeding the animals oftener than once 
a day, and as they eat mostly in the evening and during the 
night, it is desirable that the food should be placed in the 
cage late in the afternoon. For almost a year I kept a pair 
of dancers on " force "^ and water. They seemed perfectly 
healthy and were active during the whole time, but they pro- 
duced no young. If the animals are kept as pets, and breed- 
ing is not desired, a diet of "force," ''egg-o-see,"^ and crackers, 
with some bird-seed every few days, is Hkely to prove satis- 
factory. As with other animals, a variety of food is beneficial, 
but it appears to be quite unnecessary. Too much rich food 
should not be given, and the mice should be permitted to 
dictate their own diet by reveahng their preferences. They 
eat surprisingly little for the amount of their activity. I have 
had excellent success in breeding the mice by feeding them 
a mixture of dry bread-crumbs, '' force," and sweet, clean oats 
slightly moistened with milk. The food should never be 
made soppy. A little milk added thus to the food every other 
day greatly increases fertility. About once a week a small 

^ Minot watch glasses. ^ A cereal food. 



20 The Dancing Mouse 

quantity of some green food, lettuce for example, should be 
given. It is well, I have found, to vary the diet by replacing 
the bread and ''force" at intervals with crackers and seeds. 
Usually I give the food dry every other day, except in the case 
of mice which are nursing litters. One person to whom I 
suggested that lettuce was good for the dancers lost four, 
apparently because of too much of what the mice seemed to 
consider a good thing. This suggests that it should be used 
sparingly. 

Success in keeping and breeding dancing mice depends 
upon three things: cleanliness, warmth, and food supply. 
The temperature should be fairly constant, between 60° and 
70° Fahr. They cannot stand exposure to cold or lack of 
food. If one obtains good healthy, fertile individuals, keeps 
them in perfectly clean cages with soft nesting materials, 
maintains a temperature of not far above or below 65°, and 
regularly supplies them with pure water and food which they 
like, there is not Kkely to be trouble either in keeping or breed- 
ing these delicate little creatures. Several persons who have 
reported to me difficulty in rearing the young or in keeping 
the adults for long periods have been unable to maintain 
a sufficiently high or constant temperature, or have given 
them food which caused intestinal trouble. 

The males are likely to fight if kept together, and they 
may even kill one another. A male may be kept with one 
or more females, or several females may be kept together, 
for the females rarely, in my experience, fight, and the males 
seldom harm the females. Unless the male is removed from 
the cage in which the female is kept before the young are born, 
he is likely to kill the newborn animals. When a female 
is seen to be building a nest in preparation for a litter, it is 
best to place her in a cage by herself so that she may not be 
disturbed. 



Feedings Breedijig^ and Development 2i 

The sex of individuals may be determined easily in most 
cases, at the age of lo to 12 days, by the appearance of teats 
in the case of females. 

The period of gestation is from 18 to 21 days. The maxi- 
mum number born by my dancers in any single litter was 
9, the minimum number 3. In 25 litters of which I have 
accurate records, 135 individuals were born, an average of 
5.4. The average number of males per litter was precisely 
the same, 2.7, as the number of females. 

On the birth of a litter it is well to see that the female has 
made a nest from which the young are not likely to escape, 
for at times, if the nest is carelessly made, they get out of it 
or under some of the pieces of paper which are used in its 
construction, and perish. Several times I have observed 
nests so poorly built that almost all of the young perished 
because they got too far away to find their way back to the 
mother. It is surprising that the female should not take 
more pains to keep her young safe by picking them up in 
her mouth, as does the common mouse, and carrying them to a 
place where they can obtain warmth and nourishment. This 
I have never seen a dancing mouse do. For the first day 
or two after the birth of a litter the female usually remains 
in the nest box almost constantly and eats little. About the 
second day she begins to eat ravenously, and for the next 
three or four weeks she consumes at least twice as much 
food as ordinarily. Alexander and Kreidl (3 p. 567) state 
that the female does not dance during the first two weeks 
after the birth of a litter, but my experience contradicts 
their statement. There is a decreased amount of activity 
during this period, and usually the whirling movement ap- 
pears but rarely; but in some cases I have seen vigorous 
and long-continued dancing within a few hours after the birth 
of a litter. There is a wide range of variability in this matter, 



22 The Dancing Mouse 

and the only safe statement, in the Hght of my observations, 
is that the mother dances less than usual for a few days after 
a litter is bom to her. 

The development of the young, as I have observed it in 
the cases of twenty litters, for ten of which (Table i) sys- 
tematic daily records were kept, may be sketched as follows. 
At birth the mice have a rosy pink skin which is devoid of hair 
and perfectly smooth; they are blind, deaf, and irresponsive 
to stimulation of the vibrissae on the nose. During the first 
week of post-natal life the members of a litter remain closely 
huddled together in the nest, and no dance movements are 
exhibited. The mother stays with them most of the time. 
On the fourth or fifth day colorless hairs are visible, and by 
the end of the week the body is covered with a coat which 
rapidly assumes the characteristic black and white markings 
of the race. For the first few days the hind legs are too weak 
to support the body weight, and whatever movements ap- 
pear are the result of the use of the fore legs. As soon as the 
young mice are able to stand, circling movements are exhib- 
ited, and by the end of the second week they are pronounced. 
Somewhere about the tenth day the appearance of the teats 
in the case of the females serves to distinguish the sexes 
plainly. Between the tenth and fifteenth days excitabihty, 
as indicated by restless jerky movements in the presence of 
a disturbing condition, increases markedly; the auditory 
meatus opens, and, in the case of some individuals, there are 
signs of hearing. On or after the fifteenth day the eyes 
open and the efforts to escape from the nest box rapidly 
become more vigorous. About this time the mother re- 
sumes her dancing with customary vigor, and the young, 
when they have opportunity, begin to eat of the food which 
is given to her. They now dance essentially as do the adults. 
From the end of the third week growth continues without 



Feeding, Breeding, and Development 23 

notev^orthy external changes until sexual maturity is at- 
tained, between the fourth and the sixth v^eek. For several 
weeks after they are sexually mature the mice continue to 
increase in size. 

TABLE I 

Development of the Young 



Parents 


Number in 
Litter 


Hair 
Visible 


Teats 
Visible 


Jerky 
Move- 
ments 
Appear 


Ears 
Open 


React 

TO 

Sound 


Eyes 
Open 




cf 


^ 




152+151 
152 + 151 
410 + 415 

410 + 415 
420 + 425 
210 + 215 
210 + 215 
212+ 211 
220 + 225 
220 + 225 


5 

I 

2 

4 
3 
I 
2 
3 




3 

I 
4 
2 
I 
3 
3 
4 
3 


4th day 
4th day 
5 th day 
5th day 
4th day 

5th day 
4th day 
4th day 
4th day 


9th day 
nth day 
loth day 
loth day 

nth day 
loth day 
loth day 
loth day 


13th day 
loth day 
14th day 
13th day 
1 2th day 
1 7th day 
nth day 
15th day 
1 6th day 
I '/th day 


14th day 
12th day 
15th day 
14th day 
14th day 
13th day 
14th day 
X4th day 
14th day 
13th day 


14th day 
13th day 
15th day 
14th day 
14th day 
17th day 

No 

No 

No 

No 


1 6th day 
15 th day 
1 7th day 
1 6th day 
1 6th day 
15th day 
1 6th day 
15th day 
1 5th day 
1 5th day 



A course of development very similar to that just described 
was observed by Alexander and Kreidl (3 p. 565) in three 
litters of dancing mice which contained 3,5, and 7 individuals 
respectively. These authors, in comparing the development 
of the dancer with that of the common mouse, say that at 
birth the young in both cases are about 24 mm. in length. 
The young common mouse grows much more rapidly than 
the dancer, and by the ninth day its length is about 43 mm. 
as compared with 31 mm. in the case of the dancer. Accord- 
ing to Zoth (31 p. 148) the adult dancer has a body length 
of from 7 to 7.5 cm., a length from tip of nose to tip of tail 
of from 12 to 13 cm., and a weight of about 18 grams. The 
movement of the dancer from the first tends to take the form 
of circles toward the middle of the nest ; that of the common 
mouse has no definite tendency as to direction. When the 



24 The Dancing Mouse 

common mouse does move in circles, it goes j5rst in one direc- 
tion, then in the other, and not for any considerable period 
in one direction as does the true dancer. Neither the young 
dancer nor the common mouse is able to equilibrate itself 
well for the first few days after birth, but the latter can follow 
a narrow path with far greater accuracy and steadiness than 
the former. The uncertain and irregular movements of 
the common mouse are due to muscular weakness and 
to blindness, but the bizarre movements of the young 
dancer seem to demand some additional facts as an 
explanation. 

A brief account of the development of the dancer given by 
Zoth (31 p. 149) adds nothing of importance to the descrip- 
tion given by Alexander and Kreidl. As my own observa- 
tions disagree with their accounts in certain respects, I shall 
now give, in the form of a diary, a description of the important 
changes observed from day to day in a normal litter. The 
litter which I have selected as typical of the course of develop- 
ment in the dancer grew rapidly under favorable conditions. 
I have observed many litters which passed through the various 
stages of development mentioned in this description anywhere 
from a day to a week later. This was usually due to some 
such obviously unfavorable condition as too little food or 
slight digestive or bowel troubles. According to the nature 
of the conditions of growth the eyes of the dancer open any- 
where from the fourteenth to the twentieth day. This state- 
ment may serve to indicate the degree of variability as to 
the time at which a given stage of development is reached 
by different litters. 

On July 14, 1906, No. 151 (female) and No. 152 (male) 
were mated, and on August 3 a litter of six was born to them. 
The course of the development of this litter during the first 
three weeks was as follows : — 



Feeding, Breeding, and Development 25 

I 

First day. The skin is pink and hairless, several vibrissae 
are visible on the nose and lips, but there is no definite re- 
sponse when they are touched. The mice are both blind 
and deaf, but they are able to squeak vigorously. The 
mother was not seen to dance or eat during the day. 

Second day. There is a very noticeable increase in size. 
The vibrissae are longer, but touching them still fails to cause 
a reaction. No hairs are visible on the body. The mother 
danced rapidly for periods of a minute several times while 
the record was being made. She ate very little to-day. 

Third day. Scales began to appear on the skin to-day. 
The animals are rapidly increasing in strength ; they can now 
crawl about the nest easily, but they are too weak to stand, 
and constantly roll over upon their sides or backs when they 
are placed on a smooth surface. Because of their inability 
to progress it is impossible to determine with certainty whether 
they have a tendency to move in circles. The mother was 
seen out of the nest dancing once to-day. She now eats 
ravenously. 

Fourth day. One of the six young mice was found under 
a corner of the nest this morning dead, and the others were 
scattered about the nest box. I gathered them together into 
a nest which I made out of bits of tissue paper, and the 
mother immediately began to suckle them. They are very 
sensitive to currents of air, but they do not respond to light 
or sound and seldom to contact with the vibrissae. 

Fijth day. When placed on a smooth surface, they tend 
to move in circles, frequently rolling over. When placed on 
their sides or backs, they immediately try to right themselves. 
They do not walk, for their legs are still too weak to support 
the weight of the body; instead they drag themselves about 
by the use of the fore legs. Fine colorless hairs are visible 
over the entire body surface. When the vibrissae are touched, 



26 The Dancing Mouse 

the head is moved noticeably. The mother dances a great 
deal and eats about twice as much as she did before the birth 
of the litter. 

Sixth day. Certain regions of the skin, which were slightly 
darker than the remainder on the fourth and fifth days, are 
now almost black. It is evident that they are the regions 
in which the black hair is to appear. The movement in 
circles is much more definite to-day, although most of the 
individuals are still too weak to stand on their feet steadily 
for more than a few seconds at a time. Most of their time, 
when they are first taken from the nest, is spent in trying to 
maintain or regain an upright position. The hair is now 
easily visible, and the skin begins to have a white appearance 
as a result. 

Seventh day. Although they are strong enough to move 
about the nest readily, none of the young has attempted to 
leave the nest. They huddle together in the middle of it 
for warmth. The epidermal scales, which have increased 
in number since the third day, are dropping oflf rapidly. 
Contact with the vibrissae or with the surface of the body 
frequently calls forth a motor reaction, but neither light nor 
sound produces any visible change in behavior. The black 
and white regioQs of the skin are sufficiently definite now to 
enable one to distinguish the various individuals by their 
markings. The mother was seen to dance repeatedly to-day, 
and she ate all the food that was given to her. 

Eighth day. A fold is plainly visible where later the 
eyelids will separate. The black pigment in the skin has 
increased markedly. 

Ninth day. The eyelids are taking form rapidly, but they 
have not separated. The body is covered with a thick coat 
of hair which is either pure white or black. Standing on the 
four legs is still a difficult task. 



Feedhig^ Breeding, and Development 27 

Tenth day. To-day teats are plainly visible in the case of 
four of the five individuals of the litter. Up to this time I 
had thought, from structural indications, that there were 
three males and two females ; it is now evident that there are 
four females and one male. The external ear, the pinna, is 
well formed, and has begun to stand out from the head, but 
no opening to the inner portion of the ear is present. The 
eyelids appear to be almost fully formed. 

Eleventh day. There are no very noticeable changes in ap- 
pearance except in size, which continues to increase rapidly. 
They are able to regain their normal upright position almost 
immediately when they happen to roll over. The mother 
dances as usual. 

Tweljth day. It appears to-day as if the eyes were about 
to open. The ears are still closed, and there is no evidence 
of a sense of hearing. They squeaked considerably when in 
the nest, but not at all when I took them out to note their 
development. The mother stays outside of the nest box 
much of the time now, probably to prevent the young ones 
from sucking continuously. 

Thirteenth day. One of the little mice came out of the 
nest box while I was watching the litter this morning, and 
was able to find his way back directly despite the lack of 
sight. The mice are still dependent upon the mother for 
nourishment. I have not seen any of them attempt to eat the 
food which is given to the mother. They are extremely neat 
and clean. I watched one of them wash himself this morning. 
Each foot was carefully Hcked with the tongue. There seems 
to be special care taken to keep the toes perfectly clean. 

Fourteenth day. An opening into the ear is visible to-day. 
When tested with the Galton whistle, all five responded with 
quick, jerky movements of the head and legs. They evi- 
dently hear certain tones. During the past two days the ears 



28 The Dancing Mouse 

have changed rapidly. In one of the females, which seems 
to be a little in advance of the others in development, certain 
peculiarities of behavior appeared to-day. She jumped and 
squeaked sharply when touched and sprang, out of my hand 
when I attempted to take her up. This is in marked contrast 
with her behavior previously. 

Fifteenth day. The eyes are partly opened. All of the 
members of the litter came out of the nest box this morning 
and ran around the cage, dancing frequently and trying to 
eat with the mother. Three out of the five gave auditory 
reactions on first being stimulated ; none of them responded 
to repetitions of the stimulus. All appeared to be less sensi- 
tive to sounds than yesterday. The quick, nerv^ous, jerky 
movements are very noticeable. 

Sixteenth day. The eyes of all five are fully opened. They 
dance vigorously and are outside the nest much of the time. 

Seventeenth day. No reactions to sound could be detected 
to-day. The sense of sight gives evidence of being well 
developed. The nervous jumping movements persist. 

Eighteenth day. The young mice continue to suck, al- 
though they eat of the food which is given to the mother. 
They are now able to take care of themselves. 

Nineteenth day. There are no noteworthy changes except 
increase in size and strength. 

Twentieth day. No auditory reactions were obtained to- 
day, but other forms of stimulation brought about unmis- 
takable responses. 

Twenty- first day. They are now about half grown and there 
is no other change of special interest to be recorded. Growth 
continues for several weeks. The statement made by Alexan- 
der and Kreidl to the efifect that the dancer is almost full grown 
by the thirty-first day of life is false. At that age they may 
be sexually mature, but usually they are far from full grown. 



CHAPTER III 

Behavior: Dance Movements 

The peculiarities of behavior of the dancing mouse are 
responsible alike for the widespread interest which it has 
aroused, and for its name. In a little book on fancy varieties 
of mice, in which there is much valuable information con- 
cerning the care of the animals, one who styles himself "An 
old fancier" writes thus of the behavior of the dancer: "I 
believe most people have an idea that the waltzing is a stately 
dance executed on the hind feet; this is not so. The per- 
former simply goes round and round on all fours, as fast as 
possible, the head pointing inwards. The giddy whirl, after 
continuing for about a dozen turns, is then reversed in direc- 
tion, and each performance usually occupies from one to 
two minutes. Whether it is voluntary or not, is difficult to 
determine, but I am inclined to think the mouse can refrain 
if it wishes to do so, because I never see them drop any food 
they may be eating, and begin to waltz in the midst of their 
meal. The dance, if such it can be called, generally seizes 
the mouse when it first emerges from its darkened sleeping 
place, and this would lead one to suppose that the light con- 
veys an impression of shock to the brain, through the eyes, 
which disturbs the diseased centers and starts the giddy 
gyrations. The mice can walk or run in a fairly straight line 
when they wish to do so." Some of the old fancier's state- 
ments are true, others are mere guesses. Those who have 
studied the mice carefully will doubtless agree that he has 
not adequately described the various forms of behavior of 

29 



30 The Dancing Mouse 

which they are capable. I have quoted his description as an 
illustration of the weakness which is characteristic of most 
popular accounts of animal behavior. It proves that it is not 
sufficient to watch and then describe. The fact is that he 
who adequately describes the behavior of any animal watches 
again and again under natural and experimental conditions, 
and by prolonged and patient observation makes himself so 
familiar with his subject that it comes to possess an individu- 
ality as distinctive as that of his human companions. To the 
casual observer the individuals of a strange race are almost in- 
distinguishable. Similarly, the behavior of all the animals of a 
particular species seems the same to all except the observer who 
has devoted himself whole-heartedly to the study of the subject 
and who has thus become as familiar with their life of action 
as most of us are with that of our fellow- men; for him each 
individual has its own unmistakable characteristics. 

I shall now describe the behavior of the dancing mouse in 
the light of the results of the observation of scores of indi- 
viduals for months at a time, and of a large number of ex- 
periments. From time to time I shall refer to points in the 
accounts of the subject previously given by Rawitz (25 p. 
236), Cyon (9 p. 214), Alexander and Kreidl (i p. 542), 
Zoth (31 p. 147), and Kishi (21 p. 479). 

The most striking features of the ordinary behavior of the 
dancer are restlessness and movements in circles. The 
true dancer seldom runs in a straight line for more than a. 
few centimeters, although, contrary to the statements of 
Rawitz and Cyon, it is able to do so on occasion for longer 
distances. Even before it is old enough to escape from the 
nest it begins to move in circles and to exhibit the quick, 
jerky head movements which are characteristic of the race. 
At the age of three weeks it is able to dance vigorously, and 
is incessantly active when not washing itself, eating, or sleeping. 



I 



Behavior: Dance Movements 31 

According to Zoth (31 p. 149) the sense of sight and es- 
pecially the sense of smell of the dancer "seem to be keenly 
developed; one can seldom remain for some time near the 
cage without one or another of the animals growing lively, 
looking out of the nest, and beginning to sniff around in the 
air (windet). They also seem to have strongly developed 
cutaneous sensitiveness, and a considerable amount of 
curiosity, if one may call it such, in common with their 
cousin, the white mouse." I shall reserve what I have 
to say concerning the sense of sight for later chapters. 
As for the sense of smell and the cutaneous sensitive- 
ness, Zoth is undoubtedly right in inferring from the 
behavior of the animal that it is sensitive to certain odors 
and to changes in temperature. One of the most notice- 
able and characteristic activities of the dancer is its 
sniffing. Frequently in the midst of its dancing it stops 
suddenly, raises its head so that the nose is pointed 
upward, as in the case of one of the mice of the frontis- 
piece, and remains in that position for a second or two, as 
if sniffing the air. 

The restlessness, the varied and almost incessant move- 
ments, and the peculiar excitability of the dancer have re- 
peatedly suggested to casual observers the question, why 
does it move about in that aimless, useless fashion? To 
this query Rawitz has replied that the lack of certain senses 
compels the animal to strive through varied movements to 
use to the greatest advantage those senses which it does pos- 
sess. In Rawitz's opinion the lack of hearing and orienta- 
tion is compensated for by the continuous use of sight and 
smell. The mouse runs about rapidly, moves its head from 
side to side, and sniffs the air, in order that it may see and 
smell as much as possible. In support of this interpretation 
of the restlessness of the dancer, Rawitz states that he once 



32 The Dancing Mouse 

observed similar behavior in an albino dog which was deaf. 
This suggestion is not absurd, for it seems quite probable 
that the dancer has to depend for the guidance of its move- 
ments upon sense data which are relatively unimportant in 
the common mouse, and that by its varied and restless move- 
ments it does in part make up for its deficiency in sense 
equipment. 

The dancing, waltzing, or circus course movement, as it 
is variously known, varies in form from moment to moment. 
Now an individual moves its head rapidly from side to side, 
perhaps backing a little at the same time, now it spins around 
like a top with such speed that head and tail are almost in- 
distinguishable, now it runs in circles of from 5 cm. to 30 cm. 
in diameter. If there are any objects in the cage about 
or through which it may run, they are sure to direct the 
expression of activity. A tunnel or a hole in a box calls forth 
endless repetitions of the act of passing through. When two 
individuals are in the same cage, they frequently dance to- 
gether, sometimes moving in the same direction, sometimes 
in opposite directions. Often, as one spins rapidly about a 
vertical axis, the other runs around the first in small circles ; 
or again, both may run in a small circle in the same direction, 
so that their bodies form a living ring, which, because of the 
rapidity of their movements, appears perfectly continuous. 
The three most clearly distinguishable forms of dance are 
(i) movement in circles with all the feet close together under 
the body, (2) movement in circles, which vary in diameter 
from 5 cm. to 30 cm., with the feet spread widely,' and 
(3) movement now to the right, now to the left, in figure- 
eights (00 ). For convenience of reference these types of 
dance may be called whirling, circling, and the -figure eight 
dance. Zoth, in an excellent account of the behavior of the 
dancer (31 p. 156), describes "manege movements," "solo 



I 



Behavior: Dance Movements 33 



dances," and "centre dances." Of these the first is whirling, 
the second one form of circling, and the third the dancing of 
two individuals together in the manner described above. 

Both the whirling and the circling occur to the right (clock- 
wise) and to the left (anticlockwise). As certain observers 
have stated that it is chiefly to the left and others that it is 
as frequently to the right, I have attempted to get definite 
information concerning the matter by observing a number 
of individuals systematically and at stated intervals. My 
study of this subject soon convinced me that a true conception 
of the facts cannot be got simply by noting the direction of 
turning from time to time. I therefore planned and carried 
out a series of experimental observations with twenty dancers, 
ten of each sex. One at a time these individuals were placed 
in a glass jar, 26 cm. in diameter, and the number of circle 
movements executed to the right and to the left during a period 
of five minutes was determined as accurately as possible. 
This was repeated at six hours of the day : 9 and 1 1 o'clock 
A.M., and 2, 4, 6, and 8 o'clock p.m. In order that habitua- 
tion to the conditions under which the counts of turning were 
made might not influence the results for the group, with ten 
individuals the morning counts were made first, and with the 
others the afternoon counts. No attempt was made in the 
counting to keep a separate record of the whirling and circling, 
although had it been practicable this would have been de- 
sirable, for, as soon became evident to the observer, some 
individuals which whirl in only one direction, circle in both. 
In Table 2 the results of the counts for the males are re- 
corded; in Table 3 those for the females. Each number 
in the column headed "right" and "left" indicates the total 
number of circles executed by a certain dancer in a period 
of five minutes at the hour of the day named at the head of 
the column. I may point out briefly the curiously interesting 



34 The Dmtcing Mouse 

and entirely unexpected new facts which this method of 
observation revealed to me. 

First, there are three kinds of dancers : those which whirl 
almost uniformly toward the right, those which whirl just 
as uniformly toward the left, and those which whirl about 
as frequently in one direction as in the other. To illustrate, 
No. 2 of Table 2 may be characterized as a ''right whirler," 
for he turned to the right almost uniformly. In the case of 
the 6 P.M. count, for example, he turned 285 times to the right, 
not once to the left. No. 152, on the contrary, should 
be characterized as a "left whirler," since he almost always 
turned to the left. From both of these individuals No. 210 
is distinguished by the fact that he turned now to the left, now 
to the right. For him the name "mixed whirler" seems 
appropriate. 

Second, the amount of activity, as indicated by the number 
of times an individual turns in a circle within five minutes, 
increases regularly and rapidly from 9 a.m. to 8 p.m. Ac- 
cording to the general averages which appear at the bottom 
of Table 2, the average number of circles executed by the 
males at 9 a.m. was 89.8 as compared with 207.1 at 8 p.m. 
In other words, the mice dance more in the evening than 
during the day. 

Third, as it appears in a comparison of the general aver- 
ages of Tables 2 and 3, the females dance more than the 
males, under the conditions of observation. At 9 a.m. the 
males circled 89.8 times, the females 151.0 times; at 8 p.m. 
the males circled 207.1 times, the females, 279.0 times. 

Fourth, according to the averages for the six counts made 
with each individual, as they appear in Table 4, the males 
turn somewhat more frequently to the left than to the right 
(the difference, however, is not sufficient to be considered 
significant) ; whereas, the females turn much more frequently 



Behavior : Dance Movements 



35 



TABLE 2 

Number of Whirls to the Right and to the Left during 
Five-minute Intervals as Determined by Counts made at 
Six Different Hours, for each of Ten Male Dancers 



Number 

OF 

Animal 



2 
30 

34 
36 
152 
156 
210 
220 
410 
420 



Averages 



Gen. Av. 



Right 



II 

20 

2 

194 

7 

63 

3 

168 

2 

15 



48.5 



Left 



2 

I 

16 

21 

48 

8 
9 

105 
61 

142 



41.3 



89.8 



Right 



23 

134 

2 

180 

3 
53 

7 
39 
10 

5 



45-6 



Left 



4 

I 

48 

II 

171 

9 

41 

43 

27 

214 



56.9 



102.5 



Right 



194 

109 

4 

143 

6 

27 

225 

47 

8 

16 



77-9 



Left 



I 

2 
92 
65 

79 

6 

21 

5 
103 

238 



61.2 



1391 



Number 


4 P.M. 


6 P.M. 


8 P.M. 


Animal 


Right 


Left 


Right 


Left 


Right 


Left 


2 


70 


3 


285 





237 


10 


30 


154 





107 


6 


134 


5 


34 


7 


158 


5 


.118 


6 


147 


36 


173 


14 


170 


II 


325 


19 


152 





91 


16 


210 


9 


223 


156 


85 


2 


72 


26 


139 


. 26 


210 


159 


18 


31 


82 


47 


201 


220 


45 


38 


78 


17 


69 


2,2> 


410 


9 ■ 


155 


9 


394 


24 


94 


420 


18 


243 


16 


291 


3 


320 


Averages 


72.0 


72.2 


78.9 


II5-5 


99-3 


107.8 


Gen. Av. 


144.2 


194.4 


207.1 



36 



The Dancing Mouse 



TABLE 3 

Number of Whirls to the Right and to the Left during 
Five-minute Intervals as Determined by Counts made at 
Six Different Hours, for each of Ten Female Dancers 



Number 


Q A.M. 


II A.M. 


2 P.M. 


OF 








Animal 


Right 


Left 


Right 


Left 


Right 


Left 


29 


9 


18 


17 


30 


7 


22 


33 


287 





329 


I 


352 


3 


35 


48 


15 


198 


46 


208 


14 


151 


13 


88 


7 


75 


3 


167 


157 


57 


6 


50 


45 


53 


12 


211 


218 


21 


31 


55 


66 


.5 


215 


67 


216 


33 


105 


37 


226 


225 


46 


39 


72 


49 


143 


44 


415 


^Z 





156 





34 


3 


425 


43 


296 
69.9 


12 


201 


12 


210 


Averages 


81.1 


90-5 


60.7 


91-5 


70.6 


Gen. Av. 


151.0 


151.2 


162. 1 



Number 


4 P.M. 


6 P.M. 


8 p.m. 


OF 








Animai- 


Right 


Left 


Right 


Left 


Right 


Left 


29 


33 


114 


31 


36 


45 


99 


33 


436 


7 


408 


3 


364 


2 


35 


279 


6 


165 


24 


353 


10 


151 


3 


8 


2 


285 


2 


217 


157 


52 


15 


19 


125 


51 


104 


211 


190 


7 


86 


31 


67 


250 


215 


15 


292 


45 


336 


150 


232 


225 


133 


86 


48 


39 


177 


81 


415 


268 


3 


437 


7 


382 


8 


425 


12 


242 


19 


210 


4 


192 


Averages 


142. 1 


78.0 


126.0 


109.6 


1595 


1 19- 5 


Gen. Av. 


220.1 


235-6 


279.0 



Behavior: Da7tce Movements 



37 



to the right than to the left. I do not wish to emphasize the 
importance of this difference, for it is not improbable that 
counts made with a larger number of animals, or even with 
another group of twenty, would yield different results. 

The most important results of this statistical study of turn- 
ing are the demonstration of the existence of individual 
tendencies to turn in a particular direction, and of the fact that 
the whirling increases in amount from morning to evening. 

In order to discover whether the distribution of the dancers 
among the three groups which have been designated as right, 
left, and mixed whirlers agrees in general with that indicated 
by Table 4 (approximately the same number in each group) 
I have observed the direction of turning in the case of one 
hundred dancers, including those of the foregoing tables, and 
have classified them in accordance with their behavior as 
is indicated below. 







Right 
Whirlers 


Left 
Whirlers 


Mixed 
Whirlers 


Males 


19 
12 


19 

42 


12 


Females 

Totals 


15 
27 





The left whirlers occur in excess of both the right and the 
mixed whirlers. This fact, together with the results which 
have already been considered in connection with the counts 
of turning, suggests that a tendency to whirl in a certain way 
may be inherited. I have examined my data and conducted 
breeding experiments for the purpose of ascertaining whether 
this is true. But as the results of this part of the investigation 
more properly belong in a special chapter on the inheritance 
of behavior (XVIII), the discussion of the subject may be 
closed for the present with the statement that the prepon- 



38 



The Dancing Mouse 



TABLE 4 

Average Number of Whirls to the Right and to the Left for 
THE Six Intervals of Tables 2 and 3, with a Characteriza- 
tion OF THE Animals as Right Whirlers, Left Whirlers, or 
Mixed Whirlers. 







Average No. 


Average No. 




Males 


Age 


OF Whirls 
TO Right 


OF Whirls 
TO Left 


Characterization 


2 


12 mo. 


136.7 


3-3 


Right whirler 


30 


2 mo. 


109.7 


2.5 


Right whirler 


34 


2 mo. 


4-3 


96.5 


Left whirler 


36 


2 mo. 


197-5 


23.5 


Right whirler 


152 


6 mo. 


6.8 


I37-0 


Left whirler 


156 


I mo. 


73-2 


12.8 


Right whirler 


210 


3 mo. 


78.7 


62.0 


Mixed whirler 


220 


4 mo. 


74-3 


40.2 


Mixed whirler 


410 


3 wio. 


10.3 


139.0 


Left whirler 


420 


3 mo. 


12.2 


241.3 


Left whirler 


Ave 


rage 


70.4 


75.8 


4 Right whirlers 
4 Left whirlers 
2 Mixed whirlers 


Females 










29 


2 mo. 


23-7 


53.2 


Left whirler 


33 


2 mo. 


362.7 


2.7 


Right whirler 


35 


2 mo. 


208.5 


19.2 


Right whirler 


151 


6 mo. 


50 


140.0 


Left whirler 


157 


I mo. 


47.0 


51-2 


Mixed whirler 


211 


3 mo. 


109.7 


61.5 


Mixed whirler 


215 


3 mo. 


57.8 


234-5 


Left whirler 


225 


4 mo. 


103.2 


56.3 


Mixed whirler 


415 


3 mo. 


216.7 


3.5 


Right whirler 


425 


3 mo. 


17.0 


225.2 


Left whirler 


Ave 


rage 


115.1 


84.7 


3 Right whirlers 

4 Left whirlers 
3 Mixed whirlers 



Behavior: Dance Moveme7its 39 

derance of left whirlers indicated above is due to a strong 
tendency to turn to the left which was exhibited by the in- 
dividuals of one line of descent. 

The tendency of the dancer's activity to increase in amount 
toward evening, which the results of Tables 2, 3, and 4 ex- 
hibit, demands further consideration. Haacke (7 p. 337) and 
Kishi (21 p. 458) agree that the dancing is most vigorous in 
the evening; but Alexander and Kreidl (i p. 544) assert, on 
the contrary, that the whirling of the individuals which they 
observed bore no definite relation to the time of day and 
apparently was not influenced in intensity thereby. Since the 
results of my own observations contradict many of the state- 
ments made by the latter authors, I suspect that they may 
not have watched their animals long enough to discover the 
truth. The systematic records which I have kept indicate 
that the mice remain quietly in their nests during the greater 
part of the day, unless they are disturbed or come out to 
obtain food. Toward dusk they emerge and dance with vary- 
ing intensity for several hours. I have seldom discovered one 
of them outside the nest between midnight and daylight. The 
period of greatest activity is between 5 and 10 o'clock p.m. 

Zoth states that he has observed the adult dancer whirl 
79 times without an instant's interruption, and I have counted 
as many as no whirls. It seems rather absurd to say that 
an animal which can do this is weak. Evidently the dancer 
is exceptionally strong in certain respects, although it may be 
weak in others. Such general statements as are usually 
made fail to do justice to the facts. 

The supposition that light determines the periodicity 
of dancing is not borne out by my observations, for I have 
found that the animals continue to dance most vigorously 
toward evening, even when they are kept in a room which is 
constantly illuminated. In all probabihty the periodicity 



40 The Dancing Mouse 

of activity is an expression of the habits of the mouse race 
rather than of the immediate influence of any environmental 
condition. At some time in the history of the dancer hght 
probably did have an influence upon the period of activity; 
but at present, as a result of the persistence of a well-estab- 
lished racial tendency, the periodicity of dancing depends to 
a greater extent upon internal than upon external conditions. 
During its hours of quiescence it is possible to arouse the 
dancer and cause it to whirl more or less vigorously by stimu- 
lating it strongly with intense light, a weak electric current, 
or by placing two individuals which are strangers to one 
another in the same cage; but the dancing thus induced is 
seldom as rapid, varied, or as long-continued as that which 
is characteristic of the evening hours. 

One of the most interesting results of this study of the 
direction of turning, from the observer's point of view, is 
the demonstration of the fact that the truth concerning even 
so simple a matter as this can be discovered only by long and 
careful observation. The casual observer of the dancer gets 
an impression that it turns to the left more often than to the 
right ; he verifies his observation a few times and then asserts 
with confidence that such is the truth about turning. That 
such a method of getting knowledge of the behavior of the ani- 
mal is worse than valueless is clear in the light of the results 
of the systematic observations which have just been reported. 
But, however important the progress which we may have 
made by means of systematic observation of the phenomenon 
of turning, it must not for one moment be supposed that the 
whole truth has been discovered. Continued observation 
• will undoubtedly reveal other important facts concerning 
circling, whirling, and the periodicity of dancing, not to men- 
tion the inheritance of peculiarities of dancing and the sig- 
nificance of the various forms of activity. 



CHAPTER IV 
Behavior: Equilibration and Dizziness 

Quite as interesting and important as the general facts 
of behavior which we have been considering are the results 
of experimental tests of the dancer's ability to maintain its 
position under unusual spatial conditions — to climb, cross 
narrow bridges, balance itself on high places. Because of its 
tendency to circle and whirl, to dart hither and thither rapidly 
and apparently without control of its movements, the study 
of the mouse's ability to perform movements which demand 
accurate and delicate muscular coordination, and to control 
its expressions of activity, are of peculiar scientific interest. 

That observers do not entirely agree as to the facts in this 
field is apparent from the following comparison of the state- 
ments made by Cyon and Zoth (31 p. 174). 

Cyon states that the dancer 

Cannot run in a straight line. 
Cannot turn in a narrow space, 
Cannot run backward, 
Cannot run up an incline, 

Cannot move about safely when above the ground, because of 
fear and visual dizziness, 
Can hear certain tones. 

Zoth, on the contrary, maintains that the animal 

Can run in a straight line for at least 20 cm., 
Can and repeatedly does turn in a narrow space, 
Can run backward, for he has observed it do so, 

41 



42 The Dancing Mouse 

Can run up an incline unless the surface is too smooth for it to 
gain a foothold, 

Can move about safely when above the ground, and gives no 
signs of fear or dizziness, 

Cannot hear, or at least gives no signs of sensitiveness to sounds. 

Such contradictory statements (and unfortunately they 
are exceedingly common) stimulated me to the repetition of 
many of the experiments which have been made by other 
investigators to test the dancer's behavior in unusual spatial 
relations. I shall state very briefly the general conclusions 
to which these experiments have led me, with only sufficient 
reference to methods and details of results to enable any one 
who wishes to repeat the tests for himself to do so. For the 
sake of convenience of presentation and clearness, the facts 
have been arranged under three rubrics: equilibrational 
ability, dizziness, and behavior when blinded. To our 
knowledge of each of these three groups of facts important 
contributions have come from the experiments of Cyon 
(9 p. 220), Alexander and Kreidl (i p. 545), Zoth (31 p. 157), 
and Kishi (21 p. 482), although, as has been stated, in many 
instances their results are so contradictory as to demand 
reexamination. All in all, Zoth has given the most satis- 
factory account of the behavior and motor capacity of the 
dancer. 

If the surface upon which it is moving be sufficiently soft 
or rough to furnish it a foothold, the dancer is able to run 
up or down inclines, even though they be very steep, to cross 
narrow bridges, to balance itself at heights of at least 30 cm. 
above the ground, and even to climb up and down on rods, 
as is shown by certain of Zoth's photographs which are re- 
produced in Figure 4. Zoth himself says, and in this I am 
able fully to agree with him on the basis of my own obser- 
vations, "that the power of equilibration in the dancing 






[JRE 4. — Zoth's photographs of dancers crossing bridges and climbing rods. Reproduced from 

P finger's Archiv, Bd. 86. 



44 Tlie Dancing Mouse 

mouse, is, in general, very complete. The seeming reduction 
which appears under certain conditions should be attributed, 
not to visual dizziness, but in part to excitabihty and rest- 
lessness, and in part to a reduced muscular power" (31 p. i6i). 




Figure 5 . — Tracks of common mouse. Reproduced from Alexander 
and Kreidl's figure in Pjluger's Archiv, Bd. 82. 

The dancer certainly has far less grasping power than the 
common mouse, and is therefore at a disadvantage in moving 
about on sloping surfaces. One evidence of this fact is the 
character of the tracks made by the animal. Instead of 
raising its feet from the substratum and placing them neatly, 
as does the common mouse (Figure 5), it tends to shuffle along, 




Figure 6. — Tracks of dancing mouse. Reproduced from Alexander 
and Kreidl's figure in Pfliiger's Archiv, Bd. 82. 

dragging its toes and thus producing on smoked paper such 
tracks as are seen in Figure 6. From my own observations 
I am confident that these figures exaggerate the differences. 
My dancers, unless they were greatly excited or moving under 
conditions of stress, never dragged their toes as much as is 
indicated in Figure 6. However, there can be no doubt that 
they possess less power of grasping with their toes than do 
common mice. The animal is still further incapacitated 



Behavior: Equilibration and Dizziness 45 

for movement on inclined surfaces or narrow places by its 
tendency to move in circles and zigzags. The results of 
my own experiments indicate that the timidity of the adult 
is greater than that of the immature animal when it is placed 
on a bridge i or 2 cm. wide at a distance of 20 cm. from the 
ground. Individuals three weeks old showed less hesitation 
about trying to creep along such a narrow pathway than did 
full-grown dancers three or four months old ; and these, in 
turn, were not so timid apparently as an individual one year 
old. But the younger animals fell off more frequently than 
did the older ones. 

Additional support for these statements concerning equili- 
brational ability is furnished by the observations of Kishi 
(21 p. 482). He built a wooden bridge 60 cm. long, i cm. 
wide at one end, and J cm. at the other, and supported it 
at a height of 30 cm. above the ground by posts at the ends. 
On this bridge ten dancers were tested. Some attempted 
to move sidewise, others began to whirl and fell to the ground ; 
only one of the ten succeeded in getting all the way across 
the bridge on the first trial. The second time he was tested 
this individual crossed the bridge and found the post; and 
the third time he crossed the bridge and cHmbed down the 
post directly. The others did not succeed in descending the 
post even after having crossed the bridge safely, but, instead, 
finally fell to the floor from awkwardness or exhaustion. On 
the basis of these and other similar observations, Kishi says 
that the dancer possesses a fair degree of ability to orient and 
balance itself. 

Inasmuch as equilibration occurs similarly in darkness 
and in daylight, Zoth thinks that there is neither visual dizzi- 
ness nor fear of heights. But it is doubtful whether he is 
right concerning fear. There is no doubt in my mind, in 
view of the way the mice behave when placed on an elevated 



46 The Dancing Mouse 

surface, that they are timid ; but this is due probably to the 
uncomfortable and unusual position rather than to percep- 
tion of their distance from the ground. That they lack 
visual dizziness seems fairly well established. 

When rotated in a cyclostat ^ the dancer, unhke the com- 
mon mouse, does not exhibit symptoms of dizziness. The 
following vivid description of the behavior of both kinds of 
mice when rotated is given by Alexander and Kreidl (i p. 548). 
I have not verified their observations. 

The common mouse at first runs with increasing rapidity, 
as the speed of rotation of the cyclostat cylinder is increased, 
in the direction opposite to that of the cylinder itself. This 
continues until the speed of rotation has increased to about 
60 revolutions per minute. As the rotation becomes still 
more rapid the mouse begins to crawl along the floor, its 
body stretched out and clinging to the floor. At a speed of 
250 revolutions per minute it lies flat on the floor with its 
limbs extended obHquely to the movement of rotation, and 
at times with its back bent against the axis of the cylinder; 
in this position it makes but few and feeble efforts to crawl 
forward. When the rotation is suddenly stopped, the animal 
pulls itself together, remains for some seconds with extended 
limbs lying on the floor, and then suddenly falls into convul- 
sions and trembles violently. After several attacks of this 
kind, cramps appear and, despite its resistance, the animal 
is thrown about, even into the air at times, as if by an external 
force. This picture of the position assumed during rapid 
rotation, and of cramps after the cessation of rotation (the 
typical picture of rotation dizziness), is repeated with great 
uniformity in the case of the common mouse. Within fif- 
teen minutes after being returned to its cage the animal re- 

^ An apparatus consisting of a glass cylinder with a mechanism for turn- 
ing it steadily and at different speeds about its vertical axis. 



Behavior: Equilibratio7i and Dizziness 47 

covers from the effects of its experience. This description 
of the symptoms of rotation dizziness in the common mouse 
apphes equally well to the blinded and the seeing animal. 

In sharp contrast with the behavior of the common mouse 
in the cyclostat is that of the dancer. As the cylinder begins 
to rotate the dancer runs about as usual in circles, zigzags, 
and figure-eights. As the speed becomes greater it naturally 
becomes increasingly difficult for the mouse to do this, but 
it shows neither discomfort nor fear, as does the common 
mouse. Finally the centrifugal force becomes so great that 
the animal is thrown against the wall of the cylinder, where 
it remains quietly without taking the oblique position. When 
the cyclostat is stopped suddenly, it resumes its dance move- 
ments as if nothing unusual had occurred. It exhibits no 
signs of dizziness, and apparently lacks the exhaustion which 
is manifest in the case of other kinds of mice after several 
repetitions of the experiment. The behavior of the blinded 
dancer is very similar. 

If these statements are true, there is no reason to believe 
that the dancer is capable of turning or rotation dizziness. 
If it were, its daily life would be rendered very uncomfortable 
thereby, for its whirling would constantly bring about the 
condition of dizziness. Apparently, then, the dancer differs 
radically from most mammals in that it lacks visual and 
rotational dizziness. In the next chapter we shall have to 
seek for the structural causes for these facts. 

The behavior of the blinded animal is so important in its 
bearings upon the facts of orientation and equilibration that 
it must be considered in connection with them. Cyon in- 
sists that the sense of vision is of great importance to the dancer 
in orienting and equilibrating itself. When the eyes are 
covered with cotton wads fastened by collodion, this writer 
states (9 p. 223) that the mice behave as do pigeons and frogs 



48 The Dancing Mouse 

whose semicircular canals have been destroyed. They per- 
form violent forced movements, turn somersaults forward 
and backward, run up inclines and fall over the edges, and 
roll over and over. In a word, they show precisely the kind 
of disturbances of behavior which are characteristic of ani- 
mals whose semicircular canals are not functioning nor- 
mally. Cyon, however, observed that in certain dancers 
these peculiarities of behavior did not appear when they 
were blinded, but that, instead, the animals gave no other 
indication of being inconvenienced by the lack of sight than 
do common white mice. This matter of individual differences 
we shall have to consider more fully later. 

No other observer agrees with Cyon in his conclusions 
concerning vision, or, for that matter, in his statements con- 
cerning the behavior of the blind dancer. Alexander and 
Kreidl (i p. 550) contrast in the following respects the behavior 
of the white mouse and that of the dancer when they are 
blinded. The white mouse runs less securely and avoids 
obstacles less certainly when deprived of vision. The dancer 
is much disturbed at first by the shock caused by the removal 
of its eyes, or in case they are covered, by the presence of 
the unusual obstruction. It soon recovers sufficiently to 
become active, but it staggers, swerves often from side to 
side, and frequently falls over. It moves clumsily and more 
slowly than usual. Later these early indications of blindness 
may wholly disappear, and only a slightly impaired ability 
to avoid obstacles remains. 

It was noted by Kishi (21 p. 484) that the dancer when 
first blinded trembles violently, jumps about wildly, and rolls 
over repeatedly, as Cyon has stated ; but Kishi believes that 
these disturbances of behavior are temporary effects of the 
strong stimulation of certain reflex centers in the nervous 
system. After having been blinded for only a few minutes 



Behavior: Equilibratio7i and Dizziness 49 

the dancers observed by him became fairly normal in their 
behavior. They moved about somewhat more slowly than 
usually, especially when in a position which required accu- 
rately coordinated movements. He therefore fully agrees 
with Alexander and Kreidl in their conclusion that vision is 
not so important for the guidance of the movements of the 
dancer as Cyon believes. 

In summing up the results of his investigation of this 
subject Zoth well says (31 p. 168), "the orientation of the 
positions of the body with respect to the horizontal and verti- 
cal planes seems to take place without the assistance of the 
sense of sight." And, as I have already stated, this excellent 
observer insists that the ability of the dancer to place its 
body in a particular position (orientation), and its ability 
to maintain its normal relations to its surroundings (equiH- 
bration) are excellent in darkness and in daylight, provided 
only the substratum be not too smooth for it to gain a foot- 
hold. 

It must be admitted that the contradictions which exist 
in the several accounts of the behavior of the dancer are too 
numerous and too serious to be explained on the basis of 
careless observation. Only the assumption of striking in- 
dividual differences among dancers or of the existence of 
two or more varieties of the animal suffices to account for 
the discrepancies. That there are individual or variety 
differences is rendered practically certain by the fact that 
Cyon himself worked with two groups of dancers whose 
peculiarities he has described in detail, both as to structure 
and behavior. 

In the case of the first group, which consisted of three in- 
dividuals, the snout was more rounded than in the four 
individuals of the second group, and there were present on the 
head three large tufts of bristly black hair which gave the 



CO The Dancing Mouse 

mice a very comical appearance. The animals of the second 
group resembled more closely in appearance the common 
albino mouse. They possessed the same pointed snout and 
long body, and only the presence of black spots on the head 
and hips rendered them visibly different from the albino 
mouse. 

In behavior the individuals of these two groups differed 
strikingly. Those of the first group danced frequently, 
violently, and in a variety of ways ; they seldom climbed on 
a vertical surface and when forced to move on an incline they 
usually descended by sliding down backwards or sidewise 
instead of turning around and coming down head first; 
they gave no signs whatever of hearing sounds. Those of 
the second group, on the contrary, danced very moderately 
and in few ways; they climbed the vertical walls of their 
cage readily and willingly, and when descending from a 
height they usually turned around and came down head first ; 
two of the four evidently heard certain sounds very well. 
No wonder that Cyon suggests the possibihty of a different 
origin ! It seems not improbable that the individuals of the 
second group were of mixed blood, possibly the result of 
crosses with common mice. 

As I shall hope to make clear in a subsequent discussion 
of the dancer's peculiarities of behavior, in a chapter on 
individual differences, there is no sufficient reason for doubt- 
ing the general truth of Cyon's description, although there 
is abundant evidence of his inaccuracy in details. If, for 
the present, we accept without further evidence the statement 
that there is more than one variety of dancer, we shall be able 
to account for many of the apparent inaccuracies of descrip- 
tion which are to be found in the literature on the animal. 

As a result of the examination of the facts which this 
chapter presents we have discovered at least six important 



Behavior: Equilibration and Dizziness 51 

peculiarities of behavior of the dancer which demand 
an explanation in terms of structure. These are: (i) the 
dance movements — whirling, circhng, figure- eights, zigzags; 
(2) restlessness and the quick, jerky movements of the 
head; (3) lack of responsiveness to sounds; (4) more or less 
pronounced deficiency in orientational and equilibrational 
power; (5) lack of visual dizziness; (6) lack of rotational 
dizziness. 

Naturally enough, biologists from the first appearance of 
the dancing mouse in Europe have been deeply interested 
in what we usually speak of as the causes of these peculiarities 
of behavior. As a result, the structure of those portions of 
the body which are supposed to have to do with the control 
of movement, with the phenomena of dizziness, and with 
the ability to respond to sounds, have been studied thor- 
oughly. In the next chapter we shall examine such facts of 
structure as have been discovered and attempt to correlate 
them with the facts of behavior. 



CHAPTER V 
Structural Peculiarities and Behavior 

The activities of an animal are expressions of changes 
which occur in its structure, and they can be explained satis- 
factorily only when the facts of structure are known. Such 
pecuHarities of activity as are exhibited by the dancing 
mouse, as contrasted with the common mouse, suggest 
at once that this creature has a body which differs in 
important respects from that of the ordinary mouse. In 
this chapter I shall present what is known concerning the 
structural bases for the whirhng, the lack of equilibrational 
ability and of dizziness, the quick jerky head movements, 
the restlessness, and the partial or total deafness of the 
dancing mouse. 

Comparative physiologists have discovered that the ability 
of animals to regulate the position of the body with respect to 
external objects and to respond to sounds is dependent in 
large measure upon the groups of sense organs which collec- 
tively are called the ear. Hence, with reason, investigators 
who sought structural facts with which to explain the forms 
of behavior characteristic of the dancer turned their atten- 
tion first of all to the study of the ear. But the ear of the ani- 
mal is not, as might be supposed on superficial examination, a 
perfectly satisfactory natural experiment on the functions of this 
groupof sensory structures, for it is extremely uncertain whether 
any one of the usual functions of the organ is totally lacking. 
Dizziness may be lacking, and in the adult hearing also, but 

52 



Structural Peculiarities and Behavior 53 

in general the functional facts lead the investigator to expect 
modifications of the sense organs rather than their absence. 

I shall now give an account of the results of studies concern- 
ing the structure of the ear and brain of the dancer. Since 
the descriptions given by different anatomists contradict one 
another in many important points, the several investigations 
which have been made may best be considered chronologi- 
cally. 

Bernhard Rawitz (25 p. 239) was the first investigator 
to describe the structure of the ear of the Japanese or Chinese 
dancers, as he calls them. The definite problem which he 
proposed to himself at the beginning of his study was, what 
is the structural basis of the whirling movement and of the 
deafness of the mice? 

In his first paper Rawitz described the form of the ears 
of five dancers. His method of work was to make micro- 
scopic preparations of the ears, and from the sections, by 
the use of the Born method, to reconstruct the ear in wax. 
These wax models were then drawn for the illustration of the 
author's papers (Figures 8, 9, 10). 

The principal results of the early work of Rawitz are 
summed up in the following quotation from his paper: ''The 
Japanese dancing mice have only one normal canal and that 
is the anterior vertical. The horizontal and posterior ver- 
tical canals are crippled, and frequently they are grown 
together. The utriculus is a warped, irregular bag, whose 
sections have become unrecognizable. The utriculus and 
sacculus are in wide-open communication with each other 
and have almost become one. The utriculus opens broadly 
into the scala tympani, and the nervous elements of the 
cochlea are degenerate. 

"The last- mentioned degeneration explains the deafness 
of the dancing mice; but in my opinion it is a change of 



54 The Dancing Mouse 

secondary nature. The primary change is the broad open« 
ing between the utriculus and the scala tympani from which 
results the streaming of the endolymph from the semicircular 
canals into the cochlea. When, as a consequence of the 
rapid whirling movements, a great part of the endolymph is 
hurled into the scala tympani, the organ of Corti in the scala 
vestibuli is fixed and its parts are rendered incapable of 
vibration. The condition of atrophy which is observable 
in the sense cells and in the nerve elements is probably due 

Ampulla externa 



Ampulla 

anterior Eanlus utriculi 




Membrana 
basilaris 



Lagena 



Canalis 
utriculo- 
saccularis __ __ _ 

Membrana 
Ampiilla Macula acustica basilaris 

posterior sacculi 

Figure 7. — The inner ear of the rabbit. Reproduced from Selenka after 

Retzius, 

to the impossibility of functional activity; it is an atrophy 
caused by disuse " (25 p. 242). 

To render the terms which occur in this and subsequent 
descriptions of the ear of the dancer somewhat more intelli- 
gible to those who are not familiar with the general anatomy 
of the vertebrate ear, a side view of the inner ear of the rabbit 
is reproduced from a drawing by Retzius (Figure 7). I have 
chosen the ear of the rabbit for this purpose, not in preference 



Structural Peculiarities and Behavior 55 

to that of the common mouse, but simply because I failed 
to find any reliable description of the latter with drawings 
which could be reproduced. The rabbit's ear, however, is 
sufficiently like that of the mouse to make it perfectly satis- 
factory for our present purpose. 

This drawing of the rabbit's ear represents the three semi- 
circular canals, which occur in the ear of all mammals, and 
which are called, by reason of their positions, the anterior 
vertical, the posterior vertical, and the horizontal. Each 
of these membranous canals possesses at one end, in an 
enlargement called the ampulla, a group of sense cells. In 
Figure 7 the ampullae of the three canals are marked respec- 
tively, ampulla anterior, ampulla posterior, and ampulla 
externa. This figure shows also the cochlea, marked lagena, 
in which the organ of hearing of mammals (the organ of 
Corti) is located. The ear sac, of which the chief divisions 
are the utriculus and the sacculus, with which the canals 
communicate, is not shown well in this drawing. 

Within a few months after the publication of Rawitz's 
first paper on the structure of the dancer's ear, another 
European investigator, Panse (23 and 24) published a short 
paper in which he claimed that previous to the appearance 
of Rawitz's paper he had sectioned and mounted ears of the 
common white mouse and the dancing mouse side by side, 
and, as the result of careful comparison, found such slight 
differences in structure that he considered them unworthy 
of mention. Panse, therefore, directly contradicts the state- 
ments made by Rawitz. In fact, he goes so far as to say that 
he found even greater differences between the ears of different 
white mice than between them and the ears of the dancer 
(23 p. 140). 

In a somewhat later paper Panse (24 p. 498) expresses his 
belief that, since there are no peculiarities in the general form, 



56 



The Dancing Mouse 




..-C.s. 



sensory structures, or nerve supply of the ear of the dancer, 
which serve to explain the behavior of the animal, it is prob- 
able that there are unusual structural conditions in the brain, 
perhaps in the cerebellum, to which are due the dance move- 
ments and the deafness. The work of Panse is not very con- 
vincing, however, for his figures are poor and his descriptions 

meager ; neverthe- 
less, it casts a cer- 
tain amount of 
doubt upon the 
reliability of the 
descriptions given 
by Rawitz. 

The unfavorable 
light in which his 
report was placed 
by Panse's state- 
ments led Rawitz 
to examine ad- 
ditional prepara- 
tions of the ear of the dancer. Again he used the recon- 
struction method. The mice whose ears he studied were 
sent to him by the physiologist Cyon. 

As has been noted in Chapter IV, Cyon discovered certain 
differences in the structure and in the behavior of these 
dancers (ii p. 431), which led him to classify them in two 
groups. The individuals of one group climbed readily on the 
vertical walls of their cages and responded vigorously to sounds ; 
those of the other group could not climb at all and gave 
no evidences of hearing. After he had completed his study 
of their behavior, Cyon killed the mice and sent their heads 
to Rawitz ; but unfortunately those of the two groups became 
mixed, and Rawitz was unable to distinguish them. When 



Figure 8. — The membranous labyrinth of the 
dancer's ear. Type I. This figure, as well as 9 and 
ID, are reproduced from Rawitz's figures in the Archiv 
fur Anatomic und Physiologic, Physiologischc Abthei- 
lung, 1899. C.S., anterior vertical canal; C.p., posterior 
vertical canal; C.c, horizontal canal; U., utriculus. 



Structural Peculiarities and Behavior 57 



C.e-.-'- 




FiGURE 9. — The membranous labyrinth 
of the dancer's ear. Type II. 



he examined the structure of the ears of these mice, Rawitz did 
find, according to his accounts, two structural types between 
which very marked differ- 
ences existed. Were it not 
for the carelessness which is 
indicated by the confusion of 
the materials, and the influ- 
ence of Cyon's suggestion 
that there should be different 
structures to account for the 
differences in behavior, Ra- 
witz's statements might be 
accepted. As matters stand 
there can be no doubt of in- 
dividual differences in behavior, external appearance, and the 
structure of the ear ; but until these have been correlated on the 

basis of thorough- 
going, careful ob- 
servation, it is 
scarcely worth 
while to discuss 
their relations. 

To his previous de- 
scription of the con- 
ditions of the ear 
sacs, sense organs, 
and nerve elements of the dancer's ear, Rawitz adds nothing 
of importance in his second paper (26 p. 171). He merely 
reiterates his previous statements concerning the form of the 
canals, on the^Dasis of his findings in the case of six additional 
dancers. Figures 8, 9, and 10 are reproduced from Rawitz to 
show the anatomical conditions which he claims that he found. 
As these figures indicate, the canals were found to be extremely 




Figure io. — The membranous labyrinth of the 
dancer's ear. Type III. 



58 



The Da7icmg Mouse 



variable, as well as unusual in form, and the sacs distorted. 
In the ears of some specimens there were only two canals, and 
in all cases they were more or less reduced in size, distorted, or 
grown together. 

The work of Rawitz was unfavorably criticised by Alex- 
ander and Kreidl (2), Kishi (21), and Baginsky (4), as well 




Figure i i . — Photograph of a wax model of the membranous 
labyrinth of the ear of the dancer. Reproduced from Baginsky's 
figure in the Centralblatt fur Physiologic, Bd. i6. 

as by Panse (23 and 24). To their criticisms Rawitz replied by 
insisting that the other investigators could not with right attack 
his statements because they had not used the reconstruction 
method. In order to test the value of this contention, and if pos- 
sible settle the question of fact, Baginsky had a model of the ear 
of the dancer constructed by a skilled preparator (Herr Spitz) 
from sections which had been prepared by the best neurological 



Structural Peculiarities and Behavior 59 

methods. This model was made eighty times the size of the ear. 
It was then reduced in the process of photographic reproduction 
to sixteen times the natural size of the ear in the mouse. Figure 
1 1 is a photograph of Baginsky 's model. It shows beyond ques- 
tion the presence of three canals of the same general form and 
relations as those of the common mouse and of other mammals. 
Baginsky's paper is brief and to the point. His criticisms 
of the work of both Cyon and Rawitz are severe, but they are 
justified in all probability by the carelessness of these investi- 
gators in the fixation of their materials. Of the five skilled his- 
tologists who have examined the ear of the dancer, Rawitz alone 
found markedly abnormal canals. It is highly probable, there- 
fore, that the canals in his preparations in some way became 
distorted before the ears were sectioned. He doubtless described 
accurately the conditions which he found, but the chances are 
that those conditions never existed in the hving animals. 

The conflicting statements of Rawitz and Panse stimulated 
interest, and as a result two other investigators, without knowl- 
edge of one another's work, began careful researches on the 
dancer's ear. One, Alexander (2 and 3), worked in coop- 
eration with the physiologist Kreidl; the other, Kishi (21), 
worked independently. The anatomical papers of Alex- 
ander and Kishi appeared at about the same time, and since 
neither contains a reference to the other, it is evident that the 
investigations were carried on almost simultaneously. Alex- 
ander's descriptions are more detailed than those of Rawitz 
and Panse, and in certain respects Kishi's are even, more 
thoroughgoing. The first paper published by Alexander 
and Kreidl (i) contains the results of observations on the habits 
and behavior of the dancers. Having examined the chief 
facts of function, these investigators attempted to discover 
the structural conditions for the pecuHarities of behavior 
which they had observed. 



6o The Dancing Mouse 

As material for their anatomical work they made use of 
four dancers, one albino mouse, and four common gray mice. 
The ears of these individuals were fixed, sectioned, and 
examined microscopically in connection with parts of the 
brain. In all, eight dancer ears and six common mouse 
ears were studied. 

Very extensive descriptions of these preparations, together 
with measurements of many important portions of the ear, 
are presented in their paper, the chief conclusions of which 
are the following : — 

1. The semicircular canals, the ampullae, the utriculus, 
and the cristas acusticae of the canals are normal in their gen- 
eral form and relations to one another as well as in their 
histological conditions (2 p. 529). This is contradictory 
of the statements made by Rawitz. 

2. There is destruction of the macula sacculi (2 p. 534). 

3. There is destruction also of the papilla basilaris coch- 
leae, with encroachment of the surrounding tissues in vary- 
ing degrees. 

4. There is diminution in the number of fibers of the 
branches and roots of the ramus superior and ramus medius 
of the eighth nerve, and the fiber bundles are very loosely 
bound together. 

5. Similarly the number of fibers in the inferior branch 
(the cochlear nerve) of the eighth nerve is very much reduced. 

6. There is moderate reduction in the size of the two 
vestibular ganglia as a result of the unusually small number 
of nerve cells. 

7. The ganglion spirale is extremely degenerate. 
There is therefore atrophy of the branches, ganglia, and 

roots of the entire eighth nerve, together with atrophy and 
degeneration of the pars inferior labyrinthii. The nerve 
endings are especially degenerate (2 p. 534). 



Structural Peculiarities and Behavior 6i 

The above structural deviations of the ear of the dancer 
from that of the common mouse may be considered as pri- 
mary or secondary according as they are inherited or acquired. 
Since, according to Alexander and Kreidl, the dancers' 
peculiarities of behavior and deafness are directly and uni- 
formly inherited, it is obvious that certain primary structural 
deviations must serve as a basis for these functional facts. 
But it is equally clear, in the opinion of Alexander and Kreidl 
(2 p. 536), that other structural pecuKarities of the dancer 
are the result of the primary changes, and in no way the 
conditions for either the dancing or the deafness. These 
authors feel confident that the facts of behavior which are to 
be accounted for are almost certainly due to the pathological 
changes which they have discovered in the nerves, ganglia, 
and especially in the peripheral nerve endings of the ear of 
the mouse (2 p. 537). 

It is further claimed by Alexander and Kreidl that there 
are very marked individual differences among the dancers 
in the structure of the ear. In some cases the otoHths and 
the sensory hairs are lacking; in others, they are present 
in the state of development in which they are found in other 
varieties of mouse. Sometimes the cochlea is much reduced 
in size ; at other times it is found to be of normal size (2 p. 
538). These variations in structure, if they really exist, 
go far toward justifying the tendency of Cyon and Alexander 
and Kreidl, as well as many other investigators, to regard 
the dancer as abnormal or even pathological. 

The functions of the ear as at present known to the com- 
parative physiologist are grouped as the acoustic and the 
non-acoustic. The cochlea is supposed on very good grounds 
to have to do with the acoustic functions, and the organs of 
the semicircular canals on equally good evidence are thought 
to have to do with such of the non-acoustic functions as 



62 The Dancing Mouse 

equilibration and orientation. Just what the functions of 
the organs of the ear sacs are is not certainly known. These 
facts are of importance when we consider the attempts made 
by Alexander and Kreidl to correlate the various peculiar- 
ities of behavior shown by the dancer with the structural 
facts which their work has revealed. This correlation is 
indicated schematically below. The physiological facts to 
be accounted for in terms of structure are presented in the 
first column, and the anatomical facts which are thought to 
be explanatory, in the second (2 p. 539). 



Function 

I Lack of sensitiveness 
to auditory stimuli. 



2 Defective equilibra- 

tional ability. 

3 Lack of turning diz- 

ziness. 



Structure 

Destruction of the papilla basilaris coch- 
leae, etc. 

Diminution of the inferior branch of the 
eighth nerve. 

Marked degeneration of the ganglion spi- 
rale. 

Destruction of the macula sacculi. 



Diminution of the branches and roots of 
the superior and middle branches of the 
eighth nerve. 

Diminution of both gangUa vestibulii and 
of the nerve cells. 
4 Normal reactions to galvanic stimulation. 



Alexander and Kreidl themselves believe that the partial 
deafness of the dancers (for they admit that the total lack 
of hearing has not been satisfactorily proved) is due to the 
defective condition of the cochlea. They account for the 
imperfect equilibrational ability of the animals by pointing 
out the structural peculiarities of the sacculus, the vestibular 
ganglia, and the peripheral nerves. Similarly, the lack of 
dizziness they suppose to be due to the diminution of the 
fibers of the nerves which supply the canal organs, the 
atrophied condition of the vestibular ganglia, and a disturb- 



Structural Peculiarities a7zd Behavior 63 

ance of the peripheral sense organs. Furthermore, there 
are no anatomical facts which would indicate a lack of gal- 
vanic dizziness (2 p. 552). 

Despite the fact that they seem to explain all the functional 
peculiarities of the dancer, the statements made by Alexander 
and Kreidl are neither satisfying nor convincing. Their 
statements concerning the structure of the ear have not been 
verified by other investigators, and their correlation of struc- 
tural with functional facts lacks an experimental basis. 

In this connection it may be worth while to mention that 
a beautiful theory of space perception which Cyon (9) had 
constructed, largely on the basis of the demonstration by 
Rawitz that the dancers have only one normal canal, is totally 
destroyed by Panse, Baginsky, Alexander and Kreidl, and 
Kishi, for all of these observers found in the dancer three 
canals of normal shape. Cyon had noted that the most 
abnormal of the voluntary as \Mell as of the forced movements 
of the dancer occur in the plane of the canal which Rawitz 
found to be most strikingly defective. This fact he con- 
nected with his observation that the fish Petromyzon, which 
possesses only two canals, moves in only two spatial dimen- 
sions. The dancer with only one functional canal in each 
ear moves in only one plane, and neither it nor Petromyzon 
is able to move far in a straight line (11 p. 444). From these 
and similar surmises, which his eagerness to construct an 
ingenious theory led him to accept as facts quite uncritically, 
Cyon concluded that the perception of space depends upon 
the number and arrangement of the semicircular canals, and 
that the dancer behaves as it does because it possesses canals 
of unusual shape and relations to one another. The absurd- 
ity of Cyon's position becomes obvious when it is shown that 
the structural conditions of which he was making use do not 
exist in the dancer. 



64 The Dancing Mouse 

The results obtained by Kishi in his study of the ear of 
the dancer differ in many important respects from those of 
all other investigators, but especially from those of Rawitz and 
Alexander and Kreidl. 

Kishi's work was evidently done with admirable carefulness. 
His methods in the preparation of his materials, so far as 
can be judged from his report, were safe and satisfactory, 
and his descriptions of results are minute and give evidence 
of accuracy and conscientious thoughtfulness. The material 
for his histological work he obtained from three different 
animal dealers. It consisted of fifteen adult and nineteen 
young dancers, and, as material for comparison, ten com- 
mon gray mice. The animals were studied first biologically, 
that their habits and behavior might be described accurately 
and so far as possible accounted for in the light of whatever 
histological results might be obtained subsequently; then 
they were studied physiologically, that the functional impor- 
tance of various organs which would naturally be supposed 
to have to do with the peculiarities of the mouse might be 
understood; and, finally, they were killed and their ears 
and portions of their brains were studied microscopically, 
that structural conditions for the biological and physiological 
facts might be discovered. 

The ear, which was studied by the use of several series 
of sections, as well as in gross dissections, is described by 
Kishi under three headings : — 

(i) The sound-receiving apparatus (auditory organs). 

(2) The static apparatus (equilibrational organs). 

(3) The sound-transmitting apparatus (ear drum, ear bones, 
etc.). 

The chief results of his structural investigation may be stated 
briefly under these three headings. In the sound-receiving 
or auditory apparatus, Kishi failed to find the important 



Structural Peculiarities and Behavior 65 

deviations from the usual structure of the mammalian ear 
which had been described by Rawitz. The latter distinctly 
says that although the organ of Corti is present in all of the 
whirls of the cochlea, the auditory cells in it are noticeably 
degenerate. Kishi does not agree with Panse's statement 
(21 p. 476) that the auditory organ of the dancer differs in 
no important respects from that of the common mouse, for 
he found that in certain regions the hair cells of the organ 
of Corti were fewer and smaller in the dancer. He therefore 
concludes that the auditory organ is not entirely normal, 
but at the same time he emphasizes the serious discrepancy 
between his results and those of Rawitz. In not one of the 
ears of the twelve dancers which he studied did Kishi find 
the direct communication between the utriculus and the scala 
tympani which Rawitz described, and such differences as 
appeared in the organ of Corti were in the nature of slight 
deviations rather than marked degenerations. 

In the outer wall of the ductus cochlearis of the dancer 
the stria vasculosa is almost or totally lacking, while in the 
gray mouse it is prominent. This condition of the stria 
vasculosa Kishi was the first to notice in the dancer; Alex- 
ander and Kreidl had previously described a similar condi- 
tion in an albino cat. If, as has been supposed by some 
physiologists, the stria vasculosa is really the source of the 
endolymph, this state of affairs must have a marked influence 
on the functions of the auditory apparatus and the static ap- 
paratus, for pressure differences between the endolymph 
and the perilymph spaces must be present. And, as Kishi 
points out, should such pressure differences be proved to 
exist, the functional disturbance in the organ of hearing 
which the lack of responses to sounds seems to indicate might 
better be ascribed to them than to the streaming of the endo- 
lymph from the canals into the cochlea as assumed by Rawitz 



66 



TJie Dancing Mouse 



h.b. 




(21 p. 477). Kishi merely suggests that the condition of 

the stria may account for the deafness of the mouse ; he does 

^ _ not feel at all 

o«c» 1 

O- ^' confident of the 

truth of his ex- 
planation, and he 
therefore prom- 
ises in his first 
paper a contin- 
uation of his 
work in an inves- 
tigation of the 
functions of the 
stria. This, how- 
ever, he seems 
not to have ac- 
compHshed thus 
far. 

The static ap- 
paratus Kishi describes as closely similar in form to that 
of the gray mouse. In none of his twelve preparations of 
the ear of the dancer did he find such abnormalities of form 
and connections in the semicircular canals as Rawitz's 
figures and descriptions represent. Rawitz states that the 
anterior canal is normal except in its lack of connection with 
the posterior and that the posterior and horizontal are much 
reduced in size. Kishi, on the contrary, insists that all of 
the three canals are normal in shape and that the usual 
connection between the anterior and the posterior canals, 
the crus simplex, exists. He justifies these statements by 
presenting photographs of two dancer ears which he care- 
fully removed from the head. Comparison of these photo- 
graphs (Figures 12 and 13) with Rawitz's drawings of the 



Figure 12. — The inner ear of the dancer. Repro- 
duced from Kishi's figure in the Zeitschrift jur wissen- 
schaftliche Zoologie, Bd. 71. c.c. crus simplex ; o.b. anterior 
vertical canal; /j.6. posterior vertical canal; a.b. horizontal 
canal. 



Structural Peculiarities and Behavior 67 

conditions of the canals and sacs as he found them (Figures 8, 9, 
and 10), and of both with the condition in the typical mamma- 
lian ear as shown by Figure 7, will at once make clear the 
meaning of Kishi's statements. That Rawitz's descriptions of 
the canals are not correct is rendered almost certain by the fact 
that Panse, Baginsky, Alexander and Kreidl, and Kishi all agree 
in describing them 
as normal in form. ^ -u ..^^mam^^' ' 

The only impor- 
tant respects in 
which Kishi found 
the membranous 
labyrinth, that is, 
the canals and the 
ear sacs, of the 

dancer to differ ^^B^» ^ .MxmiMmy a.b. 

from that of the 
gray mouse are the 
following. In the 

dancer the CUDola Figure 13. — The inner ear of the dancer, showing 
. the spiral form of the cochlea. After Kishi. 

01 the crista 

acustica is not so plainly marked and not so highly developed, 
and the raphae of the ampuUas and canals, which frequently 
are clearly visible in the gray mouse, are lacking (21 p. 478). 

The sound-transmitting apparatus of the dancer, according 
to Kishi, differs only very slightly from that of the gray mouse, 
and there is no reason to consider the differences which appear 
as important (21 p. 478). 

Almost as amusing as the way in which Cyon's theory of 
space perception disappears in the light of critical research 
is Panse's explanation of the deafness of the dancer. Fail- 
ing to find any defects in the auditory apparatus of the inner 
ear which seemed adequate to account for the obvious lack 




68 The Dancing Mouse 

of responsiveness to sounds, this investigator concluded that 
plugs of wax which he had noticed in the auditory meatus 
of the dancer excluded sounds or in some way interfered with 
the functioning of the tympanic membrane. Kishi reports 
that he found such plugs of wax in the ears of one gray mouse, 
but in none of the dancers which he examined did he discover 
them (21 p. 479). Panse's explanation of the defective hear- 
ing of the dancer neither needs nor deserves further comment. 

As one result of his investigation, Kishi is convinced that 
the dance movements are not due to peculiarities in the semi- 
circular canals and their sense organs, as Rawitz claimed, 
for the general form and finer structure of these organs in the 
dancer is practically the same as in the common mouse. 
Kishi is just as certain that the whirling is not due to defects 
in the canal organs, as Rawitz is that it is due to such struc- 
tural conditions ! It is rather surprising that any one should 
feel confident of the power of the microscope to reveal all 
those structural conditions which are important as conditions 
of function. Probably there are histological differences 
between the ear of the dancer and that of the gray mouse, 
which, although undetectable by scientific means at present, 
furnish the structural basis for the marked differences in 
behavior. As has been set forth already (p. 9), Kishi ac- 
counts for the dance movements by assuming the inheritance 
of an acquired character of behavior. This inherited ten- 
dency to dance, he thinks, has been accentuated by the con- 
finement of the mice in narrow cages and their long-continued 
movement in the wheels which are placed in the cages (21 
p. 481). 

Rawitz, Cyon, and Alexander and Kreidl felt themselves 
under the necessity of finding peculiarities of behavior in 
the dancer which could be referred to the various abnormal- 
ities of structure which they had either seen or accepted on 



Structural Peculiarities and Behavior 69 

faith ; Kishi found himself in a very different predicament, 
for he had on his hands the commonly accepted statement 
that the animals are deaf, without being able to find any 
structural basis for this defect. To avoid the difficulty he 
questions the existence of deafness ! If perchance they are 
deaf, he thinks that it is possibly because of the defect in the 
stria vasculosa. This suggestion Kishi makes despite the 
fact that our ignorance of the function of the stria renders 
it impossible for us to do otherwise than guess at its relation 
to hearing. 

We have now briefly reviewed the results of the various 
important investigations of the behavior and structure of 
the dancer. 

The observations of Cyon, Zoth, and the writer estabHsh 
beyond doubt the existence of important individual differ- 
ences in behavior if not of distinct divisions within the species 
of mouse, and the general results of the several anatomical 
investigations make it seem highly probable that the structure 
of the ear, as well as the externally visible structural features 
of the animals, vary widely. Unfortunately, the lack of agree- 
ment in the descriptions of the ear given by the different 
students of the subject renders impossible any certain corre- 
lation of structural and functional facts. That the whirling 
and the lack of dizziness and of hearing have their structural 
bases no one doubts, but whether it is in the brain itself, in 
the sense organs, or in the labyrinth, our knowledge does not 
permit us to say. With this statement Rawitz, Cyon, and 
Alexander and Kreidl would not agree, for they beheve that 
they have discovered structural peculiarities which fully 
explain the behavior of the dancer. Panse and Kishi, on 
the other hand, contend that the ear gives no structural signs 
of such peculiarities as the dancing and deafness suggest; 
they therefore look to the cerebellum for the seat of the dis- 



70 The Dancing Mouse 

turbance. With the same possibility in mind the author of 
** Fancy Varieties of Mice" writes: "These quaint little 
creatures make amusing pets for any one who is not scientific, 
or very fond of knowing 'the reason why.' In their case, 
the reason of the peculiarity which gives them their name 
is rather a sad one. It is now pretty conclusively established 
that they are no more Japanese than they are of any other 
country in particular, but that the originators of the breed 
were common fancy mice which were suffering from a disease 
of the brain analogous to the ' gid ' in sheep. In the latter, 
the complaint is caused by a parasite in the brain; in the 
case of the Waltzing Mouse, it is probably due to an hereditary 
malformation therein. Be this as it may, the breed is now 
a firmly established one, and the children of waltzing mice 
waltz hke their parents" (32 p. 45). Although it is quite 
possible that peculiarities in the central nervous system, 
rather than in the peripheral nervous system, may be respon- 
sible for the forms of behavior exhibited by the dancer, it 
must be remembered that no such peculiarities have been re- 
vealed by the examination of the central nervous system. 
The old fancier has neither better nor worse grounds for his 
belief than have Panse and Kishi. 

So far as the reliability of the anatomical work which has 
been discussed is in question, it would seem that Rawitz's 
results are rendered somewhat unsatisfactory by the careless- 
ness of Cyon in fixing the materials ; that Panse's descriptions 
and comparisons are neither careful nor detailed enough to be 
convincing ; that the work of Alexander and Kreidl, as well as 
that of Kishi, gives evidence of accuracy and trustworthiness. 
The fact that the statements of Alexander and Kreidl frequently 
do not agree with those of Kishi proves that there are serious 
errors in the work of one or another of these investigators. 
Cyon's discussion of the anatomy of the dancer is not to be 



Structural Peculiarities and Behavior 71 

taken too seriously, for by his theory of space perception and 
of a sixth sense he was unduly biased in favor of the struc- 
tural peculiarities described by Rawitz. Nevertheless, his 
discussion is not without interest, for the way in which he 
succeeded in making every structural fact which Rawitz sug- 
gested fit into his theories and help to account for the func- 
tional peculiarities which he had himself observed, is extremely 
clever and indicates a splendid scientific imagination. 

To sum up : All the facts of behavior and physiology which 
have been established lead us to expect certain marked struc- 
tural differences between the dancer and the common mouse. 
The bizarre movements, lack of equilibrational ability, and 
the nervous shaking of the head suggest the presence of 
peculiar conditions in the semicircular canals or their sense 
organs; and the lack of sensitiveness to sounds indicates 
defects in the cochlea. Yet, strange as it may seem to those 
who are not familiar with the difficulties of the study of the 
minute structure of these organs, no structural conditions 
have been discovered which account satisfactorily for the 
dancer's peculiarities of behavior. That the ear is unusual 
in form is highly probable, since three of the four investiga- 
tors who have studied it carefully agree that it differs more 
or less markedly from that of the common mouse. But, on 
the other hand, the serious lack of agreement in their several 
descriptions of the conditions which they observed renders 
their results utterly inconclusive and extremely unsatisfactory. 
The status of our knowledge of the structure of the central 
nervous system is even less satisfactory, if possible, than that 
of our knowledge of those portions of the peripheral nervous 
system which would naturally be supposed to have to do with 
such functional peculiarities as the dancer exhibits. So 
far as I have been able to learn, no investigator has carefully 
examined the brain and spinal cord in comparison with those 



72 The Dancing Mouse 

of the common mouse, and only those who have failed to find 
any structural basis for the facts of behavior in the organs 
of the ear have attempted to account for the dancer's whirl- 
ing and deafness by assuming that the cerebellum is unusual 
in structure. We are, therefore, forced to conclude that our 
knowledge of the nervous system of the dancing mouse does 
not at present enable us to explain the behavior of the animal. 

It seems highly probable to me, in the light of my observa- 
tion of the dancer and my study of the entire literature con- 
cerning the animal, that no adequate explanation of its ac- 
tivities can be given in terms of the structure of the peripheral 
or the central nervous system, or of both, but that the struc- 
ture of the entire organism will have to be taken into account. 
The dancer's physiological characteristics, in fact, suggest 
multitudinous structural peculiarities. I have confined my 
study to its behavior, not because the problems of structure 
seemed less interesting or less important, but simply because 
I found it necessary thus to limit the field of research in order 
to accomplish what I wished within a Hmited period. 

That there are structural bases for the forms of behavior 
which this book describes is as certain as it could be were 
they definitely known; that they, or at least some of them, 
are discoverable by means of our present-day histological 
methods is almost as certain. It is, therefore, obvious that 
this is an excellent field for further research. It is not an 
agreeable task to report inconclusive and contradictory 
results, and I have devoted this chapter to a brief account 
of the work that has been done by others on the structure of 
the ear of the dancer rather for the sake of presenting a com- 
plete account of the animal as it is known to-day than because 
of the value of the facts which could be stated. 



CHAPTER VI 
The Sense of Hearing 

Repeatedly in the foregoing chapters mention has been 
made of the dancer's irresponsiveness to sounds, but it has 
not been definitely stated whether this pecuHarity of behavior 
is due to deafness or to the inhibition of reaction. This chap- 
ter is concerned with the evidence which bears upon the 
problem of the existence of a sense of hearing. Again I 
may be permitted to call attention to the observations of 
other investigators before presenting the results of my own 
experiments and stating the conclusions which I have reached 
through the consideration of all available facts. 

By the results of various simple tests which he made, 
Rawitz (25 p. 238) was convinced that the adult dancer is 
totally deaf. He did not experiment with the young, but he 
says he thinks they may be able to hear, since the necessary 
structural conditions are present. This guess which Rawitz 
made on the basis of very indefinite and uncertain knowledge 
of the histology of the ear of the young dancer is of special 
interest in the light of facts revealed by my own experiments. 
Unfortunately the study of hearing made by Rawitz is casual 
rather than thorough, and although it may turn out that 
all of his statements are justified by his observations, the 
reader is not likely to get much satisfaction from his discus- 
sion of the subject. 

Inasmuch as he could discover no structural basis for 
deafness, Panse (23 p. 140) expressed himself as unwilling 

73 



74 The Dancing Mouse 

to believe that the mice are deaf, and this despite the fact 
that he observed no responses to the sounds made by a series 
of tuning forks ranging from C5 to Cg. He believes rather 
that they are strangely irresponsive to sounds and that their 
sensitiveness is dulled, possibly, by the presence of plugs of 
wax in the ears. Since another investigator, KIshi, has 
observed the presence of similar plugs of v^ax in the ears 
of common mice which could hear, there is but slight 
probability that Panse is right in considering the plugs 
of wax as the cause of the dancer's irresponsiveness to 
sounds. 

Far more thoroughgoing tests than those of Rawitz or 
Panse were made by Cyon (9 p. 218), who holds the unique 
position of being the only person on record who has observed 
the adult dancer give definite reactions to sounds. To a 
Konig Galton whistle so adjusted that it gave a tone of 
about 7000 complete vibrations per second, which is said to be 
about the pitch of the voice of the dancer, some of the ani- 
mals tested by Cyon responded unmistakably, others not at 
all. In one group of four mice, two not only reacted markedly 
to the sound of the whistle but apparently listened intently, 
for as soon as the whistle was blown they ran to the side of 
the cage and pressed their noses against the walls as if 
attempting to approach the source of the stimulus. The 
remaining two mice gave not the slightest indication that 
the sound acted as a stimulus. By the repetition of this 
sound from eight to twelve times Cyon states that he was 
able to arouse the mice from sleep. When thus disturbed, 
the female came out of the nest box before the male. Simi- 
larly when the mice were disturbed by the whistle in the 
midst of their dancing, the female was first to retreat into 
the nest box. There is thus, according to Cyon, some indi- 
cation of sex, as well as individual, differences in sensitiveness 



The Sense of Hearing 75 

to the sound of the whistle, Cyon's statement that in order 
to evoke a response the whistle must be held above the head 
of the dancer suggests at once the possibility that currents of 
air or odors instead of sounds may have been responsible for 
the reactions which he observed. The work of this investi- 
gator justifies caution in the acceptance of his statements. 
Neither the conditions under which the auditory tests were 
made nor the condition of the animals is described with suffi- 
cient accuracy to make possible the comparison of Cyon's 
work with that of other investigators. As will appear later, 
it is of the utmost importance that the influence of other 
stimuli than sound be avoided during the tests and that the 
age of the mouse be known. The conclusion reached by 
Cyon is that some dancers are able to hear sounds of about 
the pitch of their own cries. 

The fact, emphasized by Cyon, that the mice respond to 
tones of about the pitch of their own voice is of pecuHar 
interest in its relation to the additional statements made by 
the same author to the effect that the female dancer is more 
sensitive to sounds than the male, and that the males either 
do not possess a voice or are much less sensitive to disagree- 
able stimuli than the females. In the case of the dancers 
which he first studied (9 p. 218), Cyon observed that certain 
strong stimuli evoked pain cries; but later in his investiga- 
tion he noticed that four individuals, all of which were males, 
never responded thus to disagreeable stimulation (11 p. 431). 
He asks, therefore, does this mean that the males lack a 
voice or that they are less sensitive than the females? The 
fact that he did not succeed in getting a definite answer to 
this simple question is indicative of the character of Cyon's 
work. My dancers have provided me with ample evidence 
concerning the matter. Both the males and the females, 
among the dancers which I have studied, possess a voice. 



76 The Dancing Mouse 

The females, especially during periods of sexual excitement, 
are much more likely to squeak than the males. At such 
times they give their shrill cry whenever they are touched by 
another mouse or by the human hand. A slight pinching of 
the tail will frequently cause the female to squeak, but the 
male seldom responds to the same stimulus by crying out. 
The most satisfactory way to demonstrate the existence of a 
voice in the male is to subject him to the stimulating effect 
of an induced current, so weak that it is barely appreciable to 
the human hand. To this unexpected stimulus even the 
male usually responds by a sudden squeak. There can be 
no doubt, then, of the possession of a voice by both males 
and females. The males may be either less sensitive or less 
given to vocal expression, but they are quite able to squeak 
when favorable conditions are presented. The possession of 
a voice by an animal is presumptive evidence in favor of a 
sense of hearing, but it would scarcely be safe to say that 
the mice must be able to hear their own voices. Cyon, how- 
ever, thinks that some dancers can. What further evidence 
is to be had? 

Although they obtained no visible motor reactions to such 
noises as the clapping of the hands, the snapping of the 
fingers, or to the tones of tuning forks of different pitches 
and the shrill tones of the Galton whistle, Alexander and 
Kreidl (i p. 547) are not convinced of the total deafness of 
the dancer, for, as they remark, common mice which un- 
doubtedly hear do not invariably respond visibly to sounds. 
Furthermore, the anatomical conditions revealed by their 
investigation of the ear of the dancer are not such as to 
render sensitiveness to sounds impossible. They recognize 
also that the existence of the ability to produce sounds is an 
indication of hearing. They have no confidence in the re- 
sults reported by Cyon, for they feel that he did not take 



* 



The Sense of Hearing 77 

adequate precautions to guard against the action of other 
than auditory stimuli. 

Zoth (31 p. 170) has pointed out with reason and force 
that testing the sensitiveness of the mice is especially diffi- 
cult because of their restlessness. They are almost con- 
stantly executing quick, jerky movements, starting, stopping, 
or changing the direction of movement, and it is therefore 
extremely difficult to tell with even a fair degree of certainty 
whether a given movement which occurs simultaneously with 
a sound is a response to the sound or merely coincident with 
it. With great care in the exclusion of the influence of 
extraneous stimuli, Zoth tried a large number of experiments 
to test the hearing of both young and adult dancers. Not 
once did he observe an indubitable auditory reaction. As he 
says, "I have performed numerous experiments with the 
Galton whistle, with a squeaking glass stopper, with caps 
and cartridges, without being able to come to any certain 
conclusion. With reference to the Galton whistle and par- 
ticularly to the tone which was said to have been heard 
extremely well by Cyon's mice, I believe I am rather safe in 
asserting that my mice, young (12-13 days) as well as old, 
do not react to the Konig Galton whistle (7210 Vs.). They 
could not be awakened out of sleep by repetitions of 
the sound, nor enticed out of their nests, and their dancing 
could not be interrupted" (31 p. 170). Zoth's experiments 
appear to be the most careful and critical of those thus far 
considered. 

Last to be mentioned, but in many respects of greatest 
interest and value, is the work of Kishi (21 p. 482) on the 
problem of hearing. To this acute observer belongs the 
credit of calhng attention emphatically to the ear movements 
which are exhibited by the dancer. Frequently, as he re- 
marks, the ears move as if the animal were listening or trying 



78 The Dancing Mouse 

to determine the direction whence comes a sound, yet usually 
the mouse gives no other sign of hearing. That the absence 
of ordinary reactions to sounds is due to deafness, Kishi, like 
Panse, is led to doubt because his anatomical studies have 
not revealed any defects in the organs of hearing v^hich would 
seem to indicate the lack of this sense. 

This historical survey of the problem of hearing has 
brought out a few important facts. No one of the several 
investigators of the subject, with the exception of Cyon, is 
certain that the dancer can hear, and no one of them, with 
the exception of Rawitz, is certain that it cannot hear! 
Cyon almost certainly observed two kinds of dancing mice. 
Those of his dancers which exhibited exceptional abihty to 
climb in the vertical direction and which also gave good evi- 
dence of hearing certain sounds may have been hybrids result- 
ing from the crossing of the dancer with a common mouse, or 
they may have been exceptional specimens of the true dancer 
variety. A third possibility is suggested by Rawitz's belief 
in the ability of the young dancer to hear. Cyon's positive 
results may have been obtained with immature individuals. 
I am strongly inclined to believe that Cyon did observe two 
types of dancer, and to accept his statement that some of 
the mice could hear, whereas others could not. It is evident, 
in the light of our examination of the experimental results 
thus far obtained by other investigators, that neither the 
total lack of sensitiveness to sounds in the adult nor the 
presence of such sensitiveness in the young dancer has been 
satisfactorily proved. 

I shall now report in detail the results of my own study 
of the sense of hearing in the dancer As the behavior of 
the young differs greatly from that of the adult, by which is 
meant the sexually mature animal, I shall present first the 
results of my experiments with adults and later, in contrast, 



The Sense of Hearing 79 

the results obtained with mice from one to twenty-eight days 
old. 

My preliminary tests were made with noises. While care- 
fully guarding against the interference of visual, tactual, 
temperature, and olfactory stimuli, I produced noises of vary- 
ing degrees of loudness by clapping the hands together 
suddenly, by shouting, whistling, exploding pistol caps, 
striking steel bars, ringing an electric bell, and causing an- 
other mouse to squeak. To these sounds a common mouse 
usually responds either by starting violently, or by trem- 
bling and remaining perfectly quiet for a few seconds, as 
if frightened. The adult dancers which I have tested, and 
I have repeated the experiment scores of times during the 
last three years with more than a hundred different indi- 
viduals, have never given unmistakable evidence of hearing. 
Either they are totally deaf or there is a most surprising lack 
of motor reactions. 

Precisely the same results were obtained in tests made 
with the Galton whistle throughout its range of pitches, and 
with Appuun whistles which, according to their markings, 
ranged from 2000 Vs. (C4) to 48,000 (G9), but which un- 
doubtedly did not correspond at all exactly to this range, and 
with a series of Konig tuning forks which gave tones vary- 
ing in pitch from 1024 to 16,382 complete vibrations. 

I am willing to trust these experimental results the more 
fully because during all the time I have had adult dancers 
under observation I have never once seen a reaction which 
could with any fair degree of certainty be referred to an 
auditory stimulus. Never once, although I have tried re- 
peatedly, have I succeeded in arousing a dancer from sleep 
by producing noises or tones, nor have I ever been able to 
observe any influence of sounds on the dance movements. 
All of Cyon^s signs have failed with my mice. Occasionally 



8o The Dancing Mouse 

what looked like a response to some sound appeared, but 
critical observation invariably proved it to be due to some 
other cause than the auditory stimulus. A sound produced 
above the animal is very likely to bring about a motor re- 
action, as Cyon claims ; but I have always found it to be the 
result of the currents of air or odors, which usually influence 
the animal when the experimenter is holding any object above 
it. I do not wish to maintain that Cyon's conclusions are 
false; I merely emphasize the necessity for care in the 
exclusion of other stimuli. The mice are extremely sensitive 
to changes in temperature, such, for^ example, as are produced 
by the breath of the experimenter, and one must constantly 
guard against the misinterpretation of behavior. 

In a single experiment with mice over a month old, I 
observed what might possibly indicate sensitiveness to sound. 
While holding a mouse, thirty-five days old, in my hand I 
pursed my lips and made a very shrill sound by drawing in 
air; the mouse seemed to start perceptibly according to the 
indications given by my sense of touch. I repeated the 
stimulus several times and each time I could see and feel the 
animal start slightly. With two other individuals which I 
tested the reaction was less certain, and with several others 
I failed to get any indication of response. This would seem 
to prove that the three individuals which responded happened 
to be sensitive to that particular tone at the age of five weeks. 
The test is unsatisfactory because the vibrations from my 
own body may have brought about the reaction instead of 
the air vibrations produced by my lips, and I therefore merely 
mention it in the enumeration of the various experimental 
tests which I have made. 

If we should conclude from all the negative evidence that 
is available, or that could be obtained, that the dancer is 
totally deaf, it might fairly be objected that the conclusion 



The Sense of Hearing 8i 

is unsafe, since an animal does not necessarily respond to 
stimuli by a visible change in the position or relations of its 
body. Death feigning may fairly be considered a response 
to a stimulus or stimulus complex, yet there may be no sign 
of movement. The green frog when observed in the labora- 
tory usually gives no indication v^hatever, by movements that 
are readily observable, that it hears sounds which occur 
about it, but I have been able to show by means of indirect 
methods of study that it is stimulated by these same sounds.* 
Its rate of respiration is changed by the sounds, and although 
a sound does not bring about a bodily movement, it does very 
noticeably influence movements in response to other stimuli 
which occur simultaneously with the sound. I discovered 
that under certain rather simple experimental conditions the 
green frog would regularly respond to a touch on the back 
by drawing its hind leg up toward the body. Under the 
same conditions the sound of an electric bell caused no visible 
movement of the leg, but if at the instant the back was touched 
the bell was rung, the leg movement was much greater than 
that brought about by the touch alone. This suggests at 
once the desirability of studying the sense of hearing in the 
dancer by some indirect method. The animal may be 
stimulated, and yet it may not give any visible sign of the 
influence of the auditory stimulus. 

Were not the dancing so extremely variable in rapidity 
and duration, it might be used as an index of the influence of 
auditory stimuli. Cyon's statements would indicate that 
sounds interfere with the dancing, but as I obtained no 
evidence of this, I worked instead with the following indirect 
method, which may be called the method of auditory choice. 

The apparatus which was used is described in detail in 

^ "The Sense of Hearing in Frogs." Journal of Comparative Neurology 
and Psychology, Vol. XV, p. 288, 1905. 
G 



82 The Dancing Mouse 

Chapter VII, p. 92. Figures 14 and 15 will greatly aid the 
reader in understanding its essential features. Two small 
wooden boxes, identical in form and as closely similar as 
possible in general appearance, were placed in a larger box 
in such positions that a mouse was forced to enter and pass 
through one of them in order to get to the nest- box. On 
the bottom of each of these small boxes was a series of wires 
through which an electric current could be made to pass at 
the will of the experimenter. The boxes could readily be 
interchanged in position. At one side of the large wooden 
box and beyond the range of vision of the mouse was an 
electric bell which could be caused to ring whenever the 
mouse approached the entrance to one of the small boxes. 
The point of the experiment was to determine whether the 
dancer could learn to avoid the box-which-rang when it was 
approached. The method of conducting the tests was as 
follows. Each day at a certain hour the mouse was placed 
in that part of the large box whence it could escape to the 
nest-box only by passing through one of the small boxes. If 
it approached the wrong box (whether it happened to be 
the one on the right or the one on the left depended upon 
the experimenter's decision), the bell began to ring as a 
warning against entering ; if it approached the other box, all 
was silent. As motives for the choice of the box-which-did- 
not-ring both reward and punishment were employed. The 
reward consisted of freedom to return to the nest-box via the 
passage which led from the box-which-did-not-ring ; the 
punishment, which consisted of a disagreeable electric shock, 
was given whenever the mouse entered the wrong box, that 
is, the one which had the sound as a warning. Entering 
the wrong box resulted in a disagreeable stimulus and in the 
necessity of returning to the large box, for the exit to the 
nest-box by way of the passage from this box was closed. 



The Sense of Hearing 83 

My assumption, on the basis of extended study of the ability 
of the dancer to profit by experience, was that if it could 
hear the sound of the bell it would soon learn to avoid the 
box-that-rang and enter instead the one which had no sound 
associated with it. 

Systematic tests were made with No. 4 from the 3d to 
the 12th of February, inclusive, 1906. Each day the 
mouse was permitted to find his way to the nest-box through 
one of the small boxes ten times in succession. Usually the 
experimenter rang the bell alternately for the box on the 
left and the box on the right. The time required for such a 
series of experiments varied, according to the rapidity with 
which the mouse made his choice, from ten to thirty minutes. 
If in these experiments the animal approached and entered 
the right, or soundless box, directly, the choice indicated 
nothing so far as ability to hear is concerned; if it entered 
the wrong, or sounding box, despite the ringing of the bell, 
it indicated either the lack of the influence of experience or 
inability to hear the sound; but if it regularly avoided the 
box-which-sounded it thus gave evidence of ability to hear 
the sound of the bell. The purpose of the test was to deter- 
mine, not whether the mouse could learn, but whether it 
could hear. 

For ten successive days this experiment was carried on 
with No. 4 without the least indication of increasing abihty 
to avoid the wrong box by the association of the sound of 
the bell with the disagreeable electric shock and failure to 
escape to the nest-box. In fact, the experiment was dis- 
continued because it became evident that an impossible task 
had been set for the mouse. Day by day as the tests were in 
progress I noticed that the animal became increasingly afraid 
of the entrances to the small boxes; it seemed absolutely 
helpless in the face of the situation. Partly because of the 



84 The Dancing Mouse 

definiteness of the negative results obtained with No. 4 and 
partly because of the cruelty of subjecting an animal to dis- 
agreeable conditions which it is unable to avoid, the experi- 
ment was not repeated with other individuals. I have never 
conducted an experiment which gave me as much discomfort 
as this; it was like being set to whip a deaf child because it 
did not learn to respond to stimuli which it could not feel. 

By a very similar method No. 18 was tested for his sen- 
sitiveness to the noise and jar from the induction apparatus 
which was used in connection with many of my experiments 
on vision and the modifiability of behavior. In this experi- 
ment the wrong box was indicated by the buzzing sound of 
the apparatus and the slight vibrations which resulted from 
it. Although No. 18 was tested, as was No. 4, for ten suc- 
cessive days, ten trials each day, it gave no evidence of 
ability to avoid the box-which-buzzed. 

Since both direct and indirect methods of testing the hear- 
ing of the dancer have uniformly given negative results, in 
the case of mice more than five weeks old, I feel justified in 
concluding that they are totally deaf and not merely irre- 
sponsive to sounds. 

Rawitz's statements, and the fact that what may have 
been auditory reactions were obtained with a few individuals 
of five weeks of age, suggest that the mice may be able to 
hear at certain periods of life. To discover whether this is 
true I have tested the young of twenty different litters from 
the first day to the twenty-eighth, either daily or at intervals 
of two or three days. In these tests Konig forks, steel bars, 
and a Galton whistle were used. The results obtained are 
curiously interesting. 

During the first two weeks of life none of the mice which 
I tested gave any visible motor response to the various sounds 
used. During the third week certain of the individuals re- 



The Sense of Hearing 85 

sponded vigorously to sudden high tones and loud noises. 
After the third week I have seen only doubtful signs of hear- 
ing. I shall now describe in detail the method of experi- 
mentation, the condition of the animals, and the nature of 
the auditory reactions. 

Between the twelfth and the eighteenth day the auditory 
canal becomes open to the exterior. The time is very variable 
in different litters, for their rate of growth depends upon the 
amount of nourishment which the mother is able to supply. 
Without exception, in my experience, the opening to the ear 
appears before the eyes are open. Consequently visual stimuli 
usually are not disturbing factors in the auditory tests with 
mice less than sixteen days old. There is also a sudden and 
marked change in the behavior of the mice during the third 
week. Whereas, for the first fourteen or eighteen days they 
are rather quiet and deliberate in their movements when re- 
moved from the nest, some time in the third week their be- 
havior suddenly changes and they act as if frightened when 
taken up by the experimenter. They jump out of his hand, 
squeak, and sometimes show fight. This is so pronounced 
that it has attracted my attention many times and I have 
studied it carefully to determine, if possible, whether it is 
due to some profound change in the nervous system which 
thus suddenly increases the sensitiveness of the animal or to 
the development of the sexual organs. I am inclined to 
think that it is a nervous phenomenon which is intimately 
connected with the sexual condition. Within a day or two 
after it appears the mice usually begin to show auditory re- 
actions and continue to do so for three to five days. 

I shall now describe the results obtained with a few typical 
litters. A Htter born of Nos. 151 and 152 gave uniformly 
negative results in all auditory tests up to the fourteenth day. 
On that day the ears were open, and the following observa- 



86 The Dancing Mouse 

tions were recorded. The five individuals of the htter, four 
females and one male, were taken from the nest one at a 
time at 7 a.m. and placed on a piece of paper in the bright 
sunlight. The warmth of the sun soon quieted them so 
that auditory tests could be made to advantage. As soon as 
an individual had become perfectly still, the Galton whistle 
was held at a distance of about four inches from its head in 
such a position that it could not be seen nor the currents of 
air caused by it felt, and suddenly blown. Each of the five 
mice responded to the first few repetitions of this stimulus by 
movements of the ears, twitchings of the body, and jerky 
movements of the legs. The most violent reactions resulted 
when the individual was lying on its back with its legs ex- 
tended free in the air. Under such circumstances the four 
legs were often drawn together suddenly when the whistle 
was sounded. Similar responses were obtained with the lip 
sound already mentioned. Two other observers saw these 
experiments, and they agreed that there can be no doubt that 
the mice responded to the sound. The sounds which were 
effective lay between 5000 and 10,000 complete vibrations. 

On the fifteenth day the eyes were just beginning to open. 
Three of the mice responded definitely to the sounds, but the 
other two slightly, if at all. On the sixteenth day they were 
all too persistently active for satisfactory auditory tests, and 
on the seventeenth, although they were tested repeatedly 
under what appeared to be favorable conditions, no signs of 
sensitiveness were noted. Although I continued to test this 
litter, at intervals of three or four days, for two weeks longer, 
I did not once observe a response to sound. 

This was the first litter with which I obtained perfectly 
definite, clear-cut responses to sounds. That the reactive 
ability had not been present earlier than the fourteenth day 
I am confident, for I had conducted the tests in precisely 



The Sense of Hearing 87 

the same manner daily up to the time of the appearance of 
the reactions. To argue that the mice heard before the 
fourteenth day, but were unable to react because the proper 
motor mechanism had not developed sufficiently would be 
short-sighted, for if the response depended upon the develop- 
ment of such a mechanism, it is not likely that it would 
disappear so quickly. I am therefore satisfied that these 
reactions indicate hearing. 

With another litter the following results were obtained. 
On the thirteenth day each of the eight members of the litter 
responded definitely and uniformly to the Galton whistle, 
set at 5 (probably about 8000 complete vibrations), and to a 
Konig steel bar of a vibration rate of 4096 Vs. The largest 
individuals, for almost always there are noticeable differences 
in size among the members of a fitter, appeared to be most 
sensitive to sounds. 

On the fifteenth day and again on the seventeenth unmis- 
takable responses to sound were observed ; on the eighteenth 
the responses were indefinite, and on the nineteenth none 
were obtained. I continued the tests up to the twenty-eighth 
day without further indications of hearing. 

Certain individuals in this litter reacted so vigorously to 
the loud sound produced by striking the steel bar a sharp 
blow and also to the Galton whistle, during a period of five 
days, that I have no hesitation in saying that they evidently 
heard during that period of their lives. Other members of 
the litter seemed to be less sensitive; their reactions were 
sometimes so indefinite as to leave the experimenter in doubt 
about the presence of hearing. 

A third litter, which developed very slowly because of lack 
of sufficient food, first showed unmistakable reactions to 
sound on the twenty-first day. On this day only two of the 
five individuals reacted. The reactions were much more 



88 The Dancing Mouse 

obvious on the twenty-second day, but thereafter they be- 
came indefinite. 

Still another litter, which consisted of one female and four 
males, began to exhibit the quick, jerky movements, already 
mentioned, on the fourteenth day. On the morning of the 
fifteenth day three members of the litter definitely reacted to 
the tone of the steel bar, and also to the hammer blow when 
the bar was held tightly in the hand of the experimenter. 
My observations were verified by another experimenter. 
Two individuals which appeared to be very sensitive were 
selected for special tests. Their reactions were obvious on 
the sixteenth, seventeenth, and eighteenth days; on the nine- 
teenth day they were indefinite, and on the twentieth none 
could be detected. Some individuals of this litter certainly 
had the ability to hear for at least five days. 

A sixth litter of four females and two males first gave indi- 
cations of the change in behavior which by this time I had 
come to interpret as a sign of the approach of the period of 
auditory sensitiveness, on the seventeenth day. I had tested 
them almost every day previous to this time without obtaining 
evidence of hearing. The tests with the steel bar and the 
Galton whistle were continued each day until the end of the 
fourth week without positive results. To all appearances 
the individuals of this fitter were unable to hear at any time 
during the first month of life. 

Practically the same results were obtained with another 
litter of four females. The change in their behavior was 
obvious on the eighteenth day, but at no time during the 
first month did they give any satisfactory indications of 
hearing. 

In the accompanying table, I have presented in condensed 
form the results of my auditory tests in the case of twelve 
litters of young dancers. 



The Sense of Hearing 



89 



TABLE 5 
Period of Auditory Reaction in Young Dancers 





No. IN 
Litter 


Change in 
Behavior 


Ears 
Open 


Auditory Reactions 




Appear 


Disappear 


152 ^- 151 


5 


13th day 


14th day 


14th day 


1 6th day 


152 + 151 


8 


(?) 


13th day 


13th day 


17th day 


152+ 151 


5 


13th day 


13th day 


13th day 


17th day 


152 + 151 


4 


loth day 


1 2th day 


13th day 


15th day 


410 + 415 


5 


14th day 


15th day 


15th day 


19th day 


410 + 415 


6 


13 th day 


14th day 


14th day 


i8th day 


420 + 425 


2 


1 2 th day 


14th day 


14th day 


17th day 


210+ 215 


5 


17th day 


13th day 


17th day 


19th day 


210 + 215 


6 


nth day 


14th day 


No reactions 


220 + 225 


6 


i6th day 


14th day 


No reactions 


220 + 225 


6 


17th day 


13th day 


No reactions 


212 + 211 


4 


15th day 


14th day 


No reactions 



Certain of the litters tested responded definitely to sounds, 
others gave no sign of hearing at any time during the first 
four weeks of life. Of the twelve litters for which the re- 
sults of auditory tests are presented in Table 5, eight evi- 
dently passed through an auditory period. It is important 
to note that all except one of these were the offspring of 
Nos. 151 and 152, or of their descendants Nos. 410 and 415 
and Nos. 420 and 425. In fact every one of the fitters in 
this line of descent which I have tested, and they now num- 
ber fifteen, has given indications of auditory sensitiveness. 
And, on the other hand, only in a single instance have the 
litters born of Nos. 210 and 215, or of their descendants, 
given evidence of ability to hear. 

These two distinct lines of descent may be referred to 
hereafter as the 400 and the 200 lines. I have observed 
several important differences between the individuals of these 



90 The Dancing Mouse 

groups in addition to the one already mentioned. The 200 
mice were sometimes gray and white instead of black and 
white; they climbed much more readily and danced less 
vigorously than those of the 400 group. These facts are 
particularly interesting in connection with Cyon's descriptions 
of the two types of dancer which he observed. 

In criticism of my conclusion that the young dancers are 
able to hear certain sounds for a few days early in life, and 
then become deaf, it has been suggested that they cease to 
react because they rapidly become accustomed to the sounds. 
That this is not the case, is evident from the fact that the re- 
actions often increase in definiteness during the first two or 
three days and then suddenly disappear entirely. But even 
if this were not true, it would seem extremely improbable 
that the mouse should become accustomed to a sudden and 
startlingly loud sound with so few repetitions as occurred in 
these tests. On any one day the sounds were not made more 
than five to ten times. Moreover, under the same external 
condition, the common mouse reacts unmistakably to these 
sounds day after day when they are first produced, although 
with repetition of the stimulus at short intervals, the reactions 
soon become indefinite or disappear. 

The chief results of my study of hearing in the dancer 
may be summed up in a very few words. The young dancer, 
in some instances, hears sounds for a few days during the 
third week of life. The adult is totally deaf. Shortly be- 
fore the period of auditory sensitiveness, the young dancer 
becomes extremely excitable and pugnacious. 



CHAPTER VII 

The Sense of Sight: Brightness Vision 

The sense of sight in the dancer has received little atten- 
tion hitherto. In the literature there are a few casual state- 
ments to the effect that it is of importance. Zoth, for example 
(31 p. 149), remarks that it seems to be keenly developed ; and 
other writers, on the basis of their observation of the animal's 
behavior, hazard similar statements. The descriptions of 
the behavior of blinded mice, as given by Cyon, Alexander 
and Kreidl, and Kishi (p. 47), apparently indicate that the 
sense is of some value ; they do not, however, furnish definite 
information concerning its nature and its role in the daily 
life of the animal. 

The experimental study of this subject which is now to 
be described was undertaken, after careful and long- continued 
observation of the general behavior of the dancer, in order 
that our knowledge of the nature and value of the sense of 
sight in this representative of the Mammalia might be in- 
creased in scope and definiteness. The results of this study 
naturally fall into three groups: (i) those which concern 
brightness vision, (2) those which concern color vision, and 
(3) those which indicate the role of sight in the life of the 
dancer. 

Too frequently investigators, in their work on vision in 
animals, have assumed that brightness vision and color 
vision are inseparable; or, if not making this assumption, 
they have failed to realize that the same wave-length prob- 

91 



92 



The Dancing Mouse 



ably has markedly different effects upon the retinal elements 
of the eyes of unlike organisms. In a study of the sense 

of sight it is 
extremely impor- 
tant to discover 
whether difference 
in the quality, as 
well as in the in- 
tensity, of a visual 
stimulus influ- 
ences the organ- 
ism; in other 
words, whether 
color sensitive- 
ness, as well as 
brightness sensi- 
tiveness, is pres- 
ent. If the dancer 
perceives only 
brightness or lu- 
minosity, and not 
color, it is evident 
that its visual 
world is strikingly 

Figure 14. — Discrimination box. W, electric-box dllierent irom 
with white cardboards; B, electric-box with black card- that of the normal 
boards. Drawn by Mr. C. H. Toll, 1 1 • 

human being. 
The experiments now to be described were planned to show 
what the facts really are. 

As a means of testing the ability of the dancer to distin- 
guish differences in brightness, the experiment box repre- 
sented by Figures 14 and 15 was devised. Figure 14 is the 
box as seen from the position of the experimenter during the 




The Sense of Sight: Brightness Vision 93 



tests. Figure 15 is its ground plan. This box, which was 
made of wood, was 98 cm. long, 38 cm. wide, and 17 cm. 
deep, as measured on the outside. 
The plan of construction and its 
significance in connection with 
these experiments on vision will 
be clear from the following ac- 
count of the experimental 
procedure. A mouse whose 
brightness vision was to be 
tested was placed in the 
nest-box, A (Figure 15). 
Thence by pushing open 
the swinging door at /, it 
could pass into the en- 
trance chamber, B. 
Having entered B it 
could return \.oA only 
by passing through 
one of the electric- 
boxes, marked TF, 
and following the 
alley to O, where by 
pushing open the 




swing door it could 
enter the nest-box. 



I 


n 


E 1 
■ 1 


—- 


w 


W 


















""l 


R 






B 




6 


^^ I 





A 



Figure 15, — Ground plan of discrimination 
box. ^, nest-box; B, entrance chamber; W,W, 
rpv 1 .7- electric-boxes; L, doorway of left electric-box; R, 

1 ne door at 1 swung doorway of right electric-box; E, exit from electric- 
box to alley; 7, swinging door between A and 5; 
O, swinging door between alley and ^ ; /C, induc- 
tion apparatus; C, electric cell; K, key in circuit. 



inward, toward B, 

only; those at O, 

right and left, swung 

outward, toward A, only. It was therefore impossible for 

the mouse to follow any other course than A-I-B-L-W-E-0 

or A-I-B-R-W-E-0. The doors at / and O were pieces of 



94 The Dancing Mouse 

wire netting of \ cm. mesh, hinged at the top so that a mouse 
could readily open them, in one direction, by pushing with 
its nose at any point along the bottom. On the floor of 
each of the electric-boxes, W^ was an oak board i cm. in 
thickness, which carried electric wires by means of which 
the mouse could be shocked in W when the tests demanded 
it. The interrupted circuit constituted by the wires in the 
two electric- boxes, in connection with the induction appa- 
ratus, /C, the dry battery, C, and the hand key, K, was 
made by taking two pieces of No. 20 American standard 
gauge copper wire and winding them around the oak board 
which was to be placed on the floor of each electric- box. 
The wires, which ran parallel with one another, \ cm. apart, 
fitted into shallow grooves in the edges of the board, and 
thus, as well as by being drawn taut, they were held firmly 
in position. The coils of the two pieces of wire alternated, 
forming an interrupted circuit which, when the key K was 
closed, was completed if the feet of a mouse rested on points 
of both pieces of wire. Since copper wire stretches easily and 
becomes loose on the wooden base, it is better to use phosphor 
bronze wire of about the same size, if the surface covered by 
the interrupted circuit is more than three or four inches in 
width. The phosphor bronze wire is more difficult to wind 
satisfactorily, for it is harder to bend than the copper wire, 
and it has the further disadvantage of being more brittle. 
But when once placed properly, it forms a far more lasting 
and satisfactory interrupted circuit for such experiments as 
those to be described than does copper wire. In the case of 
the electric-boxes under consideration, the oak boards which 
carried the interrupted circuits were separate, and the two 
circuits were joined by the union of the wires between the 
boxes. The free ends of the two pieces of wire which con- 
stituted the interrupted circuit were connected with the 



The Sense of Sight: Brightness Vision 95 

secondary coil of a Porter inductorium whose primary coil 
was in circuit with a No. 6 Columbia dry battery. In the 
light of preliminary experiments, made in preparation for 
the tests of vision, the strength of the induced current re- 
ceived by the mouse was so regulated, by changing the posi- 
tion of the secondary coil with reference to the primary, that 
it was disagreeable but not injurious to the animal. What 
part the disagreeable shock played in the test of brightness 
vision will now be explained. 

An opportunity for visual discrimination by brightness 
difference was provided by placing dead black cardboard at 
the entrance and on the inside of one of the electric-boxes, 
as shown in Figure 14, 5, and white cardboard similarly in 
the other box. These cardboards were movable and could 
be changed from one box to the other at the will of the experi- 
menter. The test consisted in requiring the mouse to choose 
a certain brightness, for example, the white cardboard side, 
in order to return to the nest- box without receiving an 
electric shock. The question which the experimenter asked 
in connection with this test really is. Can a dancer learn to 
go to the white box and thus avoid discomfort? If we 
assume its ability to profit by experience within the limits of 
the number of experiences which it was given, such a modi- 
fication of behavior would indicate discrimination of bright- 
ness. Can the dancer distinguish white from black; light 
gray from dark gray; two grays which are almost of the 
same brightness ? The results which make up the remainder 
of this and the following chapter furnish a definite answer to 
these questions. 

To return to the experimental procedure, the mouse 
which is being tested is placed by the experimenter in the 
nest-box, where frequently in the early tests food and a 
comfortable nest were attractions. If it does not of its own 



96 The Dajicing Mouse 

accord, as a result of its abundant random activity, pass 
through / into B within a few seconds, it is directed to the 
doorway and urged through. A choice is now demanded 
of the animal ; to return to the nest- box it must enter either 
the white electric-box or the black one. Should it choose 
the white box, it is permitted to return directly to A by way 
of the doorway jE, the alley, and the swinging door at O, and 
it thus gets the satisfaction of unobstructed activity, freedom 
to whirl, to feed, and to retreat for a time to the nest. Should 
it choose to attempt to enter the black box, as it touches the 
wires of the interrupted circuit it receives a shock as a result 
of the closing of the key in the circuit by the experimenter, 
and further, if it continues its forward course instead of 
retreating from the ''stinging" black box, its passage through 
E is blocked by a barrier of glass temporarily placed there by 
the experimenter, and the only way of escape to the nest- 
box is an indirect route by way of B and the white box. 
Ordinarily the shock was given only when the mouse entered 
the wrong box, not when it retreated from it; it was never 
given when the right box was chosen. The box to be chosen, 
whether it was white, gray, or black, will be called the right 
box. The electric shock served as a means of forcing the 
animal to use its discriminating ability. But the question of 
motives in the tests is not so simple as might appear from 
this statement. 

The reader will wonder why the mouse should have any 
tendency to enter 5, and why after so doing, it should trouble 
to go further, knowing, as it does from previous experiences, 
that entering one of the electric- boxes may result in dis- 
comfort. The fact is, a dancer has no very constant tendency 
to go from A \.Q> B dX the beginning of the tests, but after it 
has become accustomed to the box and has learned what 
the situation demands, it shows eagerness to make the trip 



The Sense of Sight: Brightness Vision 97 

from A to B, and thence by way of either the right or the 
left route to A. That the mouse should be willing to enter 
either of the electric-boxes, after it has experienced the 
shock, is even more surprising than its eagerness to run from 
A to B, When first tested for brightness discrimination in 
this apparatus, a dancer usually hesitated at the entrance to 
the electric-boxes, and this hesitation increased rapidly un- 
less it were able to discriminate the boxes by their difference 
in brightness and thus to choose the right one. During the 
period of increasing hesitancy in making the choice, the 
experimenter, by carefully moving from / toward the en- 
trances to the electric- boxes a piece of cardboard which 
extended all the way across -S, greatly increased the mouse's 
desire to enter one of the boxes by depriving it of dancing 
space in B. If an individual which did not know which 
entrance to choose were permitted to run about in B^ it would 
often do so for minutes at a time without approaching the 
entrance to the boxes ; but the same individual, when con- 
fined to a dancing space 4 or 5 cm. wide in front of the 
entrances, would enter one of the electric-boxes almost im- 
mediately. This facilitation of choice by decrease in the 
amount of space for whirling was not to any considerable 
extent the result of fear, for all the dancers experimented 
with were tame, and instead of forcing them to rush into one 
of the boxes blindly and without attempt at discrimination, 
the narrowing of the space simply increased their efforts to 
discriminate. The common mouse when subjected to simi- 
lar experimental conditions is likely to be frightened by being 
forced to approach the entrances to the boxes, and fails to 
choose ; it rushes into one box directly, and in consequence 
it is as often wrong as right. The dancer always chooses, 
but its eagerness to choose is markedly increased by the 
restriction of its movements to a narrow space in front of 

H 



98 The Dancing Mouse 

the entrances between which it is required to discriminate. 
It is evident that the animal is uncomfortable in a space 
which is too narrow for it to whirl in freely. It must have 
room to dance. This furnished a sufficiently strong motive 
for the entering of the electric-boxes. It must avoid dis- 
agreeable and unfavorable stimuli. This is a basis for 
attempts to choose, by visual discrimination, the electric-box 
in which the shock is not given. It may safely be said that 
the success of the majority of the experiments of this book 
depended upon three facts: (i) the dancer's tendency to 
avoid disagreeable external conditions, (2) its escape-from- 
confinement-impelling need of space in which to dance freely, 
and (3) its abundant and incessant activity. 

Of these three conditions of success in the experiments, 
the second and third made possible the advantageous use of 
the first. For the avoidance of a disagreeable stimulus could 
be made use of effectively in the tests just because the mice 
are so restless and so active. In fact their eagerness to do 
things is so great that the experimenter, instead of having 
to wait for them to perform the desired act, often is forced 
to make them wait while he completes his observation and 
record. In this respect they are unlike most other animals. 

My experiments with the dancer differ from those which 
have been made by most students of mammalian behavior 
in one important respect. I have used punishment instead 
of reward as the chief motive for the proper performance of 
the required act. Usually in experiments with mammals 
hunger has been the motive depended upon. The animals 
have been required to follow a certain devious path, to 
escape from a box by working a button, a bolt, a lever, or 
to gain entrance to a box by the use of teeth, claws, hands, 
or body weight and thus obtain food as a reward. There are 
two very serious objections to the use of the desire for food 



The Sense of Sight: Brighhiess Vision 99 



r 

ff as a motive in animal behavior experiments — objections 
W which in my opinion render it almost worthless in the case 
of many mammals. These are the discomfort of the animal 
and the impossibility of keeping the motive even fairly con- 
stant. However prevalent the experience of starvation may 
be in the Hfe of an animal, it is not pleasant to think of sub- 
jecting it to extreme hunger in the laboratory for the sake of \ 
finding out what it can do to obtain food. Satisfactory re- 
sults can be obtained in an experiment whose success depends ■ 
chiefly upon hunger only when the animal is so hungry that \ 
it constantly does its best to obtain food, and when the 
desire for food is equally strong and equally effective as a 
spur to action in the repetitions of the experiment day after 
day. It is easy enough to get almost any mammal into a 
condition of utter hunger, but it is practically impossible to 
have the desire for food of the same strength day after day. 
In short, the desire for food is unsatisfactory as a motive in 
animal behavior work, first, because a condition of utter 
hunger, as has been demonstrated with certain mammals, 
is unfavorable for the performance of complex acts, second, 
because it is impossible to control the strength of the motive, 
and finally, because it is an inhumane method of experi- 
mentation. 

In general, the method of punishment is more satisfactory 
than the method of reward, because it can be controlled to a 
greater extent. The experimenter cannot force his subject 
to desire food; he can, however, force it to discriminate 
between conditions to the best of its knowledge and ability 
by giving it a disagreeable stimulus every time it makes a 
mistake. In other words, the conditions, .upon which the 
avoidance of a disagreeable factor in the/ enyitonment de- 
pends are far simpler and much More" -constant 'than ^. those 
upon which the seeking of an agreeable ciaetoi: depends. 



lOO The Dancmg Mouse 

Situations which are potentially beneficial to the animal 
attract it in varying degrees according to its internal condi- 
tion; situations which are potentially disagreeable or in- 
jurious repel it with a constancy which is remarkable. The 
favorable stimulus solicits a positive response; the unfavor- 
able stimulus demands a negative response. 

Finally, in connection with the discussion of motives, it is 
an important fact that forms of reward are far harder to 
find than forms of punishment. Many animals feed only at 
long intervals, are inactive, do not try to escape from con- 
finement, cannot be induced to seek a particular spot, in a 
word, do not react positively to any of the situations or con- 
ditions which are employed usually in behavior experiments. 
It is, however, almost always possible to find some disagree- 
able stimulus which such an animal will attempt to avoid. 

As it happens, the dancer is an animal which does not 
stand the lack of food well enough to make hunger a possi- 
ble motive. I was driven to make use of the avoiding re- 
action, and it has proved so satisfactory that I am now 
using it widely in connection with experiments on other 
animals. The use of the induction shock, upon which I 
depended almost wholly in the discrimination experiments 
with the dancer, requires care ; but I am confident that no 
reasonable objection to the conduct of the experiments could 
be made on the ground of cruelty, for the strength of the 
current was carefully regulated and the shocks were given 
only for an instant at intervals. The best proof of the hu- 
maneness of the method is the fact that the animals continued 
in perfect health during months of experimentation. 

The brightness^ discrimination tests demanded, in addition 
to motives f6r'<ihpicc, adequate precautions against discrimi- 
n%ticaa't)y'\?ther thaliVviitAal factors, and, for that matter, by 
other "visual' fdctQ,i!:s«'tlian that of brightness. The mouse 



The Sense of Sight: Brightness Vision loi 

might choose, for example, not the white or the black box, 
but the box which was to the right or to the left, in accord- 
ance with its experience in the previous test. This would be 
discrimination by position. As a matter of fact, the animals 
have a strong tendency at first to go uniformly either to the 
right or to the left entrance. This tendency will be exhibited 
in the results of the tests. Again, discrimination might 
depend upon the odors of the cardboards or upon slight 
differences in their shape, texture, or position. Before con- 
clusive evidence of brightness discrimination could be ob- 
tained, all of these and other possibilities of discrimination 
had to be eliminated by check tests. I shall describe the 
various precautions taken in the experiments to guard against 
errors in interpretation, in order to show the lengths to 
which an experimenter may be driven in his search for 
safely interpretable results. 

To exclude choice by position, the cardboards were moved 
from one electric-box to the other. When the change was 
made regularly, so that white was alternately on the right 
and the left, the mouse soon learned to go alternately to the 
right box and the left without stopping to notice the visual 
factor. This was prevented by changing the position of the 
cardboards irregularly. 

Discrimination by the odor, texture, shape, and position 
of the cardboards was excluded by the use of different kinds 
of cardboards, by changing the form and position of them in 
check tests, and by coating them with shellac. 

The brightness vision tests described in this chapter were 
made in a room which is lighted from the south only, with 
the experiment box directed away from the windows. The 
light from the windows shone upon the cardboards at the 
entrances to the electric-boxes, not into the eyes of the mouse 
as it approached them. Each mouse used in the experiments 



I02 The Dmuing Mouse 

was given a series of ten tests in succession daily. The ex- 
periment was conducted as follows. A dancer was placed in 
i4, where it usually ran about restlessly until it happened to 
find its way into B. Having discovered that the swing door 
at / could be pushed open, the animal seemed to take satis- 
faction in passing through into B as soon as it had been 
placed in or had returned to ^. In 5, choice of two en- 
trances, one of which was brighter than the other, was forced 
by the animal's need of space for free movement. If the 
right box happened to be chosen, the mouse returned to A 
and was ready for another test ; if it entered the wrong box, 
the electric shock was given, and it was compelled to retreat 
from the box and enter the other one instead. In the early 
tests with an individual, a series sometimes covered from 
twenty to thirty minutes ; in later tests, provided the condi- 
tion of discrimination was favorable, it did not occupy more 
than ten minutes. 

. To exhibit the methods of keeping the records of these 
experiments and certain features of the results, two sample 
record sheets are reproduced below. The first of these 
sheets, Table 6, represents the results given by No. 5, a 
female,^ in her first series of white-black tests. Table 7 
presents the results of the eleventh series of tests given to 
the same individual. 

In the descriptions of the various visual experiments of 
this and the following chapters, the first word of the couplet 
which describes the condition of the experiment, for example, 
white-black, always designates the visual condition which the 
animal was to choose, the second that which it was to avoid 
on penalty of an electric shock. In the case of Tables 6 and 
7, for example, white cardboard was placed in one box, 

^ It is to be remembered that the even numbers always designate males ; 
the odd numbers, females. 



The Sense of Sight: Brightness Vision 103 

TABLE 6 

Brightness Discrimination 

White-Black, Series i 

Experimented on No. 5 January 15, 1906 



Test 


Position 
OF Cardboards 


Right 


Wrong 


I 
2 

3 
4 
5 
6 

\ 

9 
10 


White left 
White right 
White left 
White right 
White left 
White right 
White left 
White right 
White left 
White right 


Right 
Right 

Right 

Right 


Wrong 
Wrong 
Wrong 
Wrong 

Wrong 
Wrong 


Totals 




4 


6 



black in the other, and the animal was required to enter the 
white box. In the tables the first column at the left gives 
the number of the test, the second the positions of the. card- 
boards, and the third and fourth the result of the choice. 
The first test of Table 6 was made with the white cardboard 
on the box which stood at the left of the mouse as it ap- 
proached from A, and, consequently, with the black card- 
board on the right. As is indicated by the record in the 
"wrong" column, the mouse chose the black instead of the 
white. The result of this first series was choice of the white 
box four times as compared with choice of the black box six 
times. On the eleventh day, that is, after No. 5 had been 
given TOO tests in this brightness vision experiment, she 
made no mistakes in a series of ten trials (Table 7). 

Before tests, such as have been described, can be pre- 



I04 



The Dancing Mouse 



sented as conclusive proof of discrimination, it must be 
shown that the mouse has no preference for the particular 
brightness which the arrangement of the test requires it to 
select. That any preference which the mouse to be tested 
might have for white, rather than black, or for a light gray 
rather than a dark gray, might be discovered, what may be 
called preference test series were given before the discrimi- 
nation tests were begun. These series, two of which were 
given usually, consisted of ten tests each, with the white 
alternately on the left and on the right. The mouse was 
permitted to enter either the white or the black box, as it 
chose, and to pass through to the nest-box without receiving 
a shock and without having its way blocked by the glass 
plate. The conditions of these preference tests may be 
referred to hereafter briefly as "No shock, open passages." 

TABLE 7 
Brightness Discrimination 
White-Black, Series ii 
Experimented on No. 5 February 2, 1906 



Test 


Position 
OF Cardboards 


Right 


Wrong 


I 
2 

3 
4 
5 
6 

7 
8 

9 
10 


White left 
White left 
White right 
White right 
White right 
White left 
White left 
White left 
White right 
White right 


Right 
Right 
Right 
Right 
Right 
Right 
Right 
Right 
Right 
Right 




Totals 




10 






The Sense of Sight: Brightness Vision 105 

The preference tests, which of course would be valueless as 
such unless they preceded the training tests, were given as 
preliminary experiments, in order that the experimenter 
might know how to plan his discrimination tests, and how 
to interpret his results. 

The results given in the white-black preference tests by 
ten males and ten females are presented in Table 8. Three 
facts which bear upon the brightness discrimination tests ap- 
pear from this table: (i) black is preferred by both males 
and females, (2) this preference is more marked in the first 
series of tests than in the second, and (3) it is slightly stronger 
for the first series in the case of females than in the case of 
males. 

That the dancers should prefer to enter the dark rather 
than the light box is not surprising in view of the fact that 
the nests in which they were kept were ordinarily rather 

TABLE 8 
WmxE -Black Preference Tests 





First Series 


Second Series 










White 


Black 


White 


Black 


No. 10 


3 


7 


3 


7 


18 


5 


5 


5 


5 


20 


2 


8 


4 


6 


152 


4 


6 


6 


4 


210 


4 


6 


4 


6 


214 


6 


4 


3 


7 


220 


5 


5 


3 


7 


230 


4 


6 


2 


8 


410 


4 


6 


5 


5 


420 


4 


6 


9 


I 


Averages 


4.1 


5-9 


4.4 


5-6 



io6 



The Dancing Mouse 
TABLE 8 — Continued 





First Series 


Second Series 


Females 








White 


Black 


White 


Black 


No. II 


5 


5 


4 


6 


151 


6 


4 


5 


5 


215 


2 


8 


2 


8 


213 


2 


8 


5 


5 


225 


4 


6 


2 


8 


227 


4 


6 


6 


4 


235 


6 


4 


4 


6 


415 


2 


8 


4 


6 


425 


5 


5 


8 


2 


229 


2 


8 


5 


5 


Averages 


3.8 


6.2 


4-5 


5-5 



dark. But whatever the basis of the preference, it is clear 
that it must be taken account of in the visual discrimination 
experiments, for an individual which strongly preferred 
black might choose correctly, to all appearances, in its first 
black-white series. Such a result would demonstrate pref- 
erence, and therefore one kind of discrimination, but not 
the formation of a habit of choice by discrimination. The 
preference for black is less marked in the second series of 
tests because the mouse as it becomes more accustomed to 
the experiment box tends more and more to be influenced by 
other conditions than those of brightness. The record sheets 
for both series almost invariably indicate a strong tendency 
to continue to go to the left or the right entrance according 
to the way by which the aaimal escaped the first time. This 
cannot properly be described as visual choice, for the mouse 
apparently followed the previous course without regard to 
the conditions of illumination. We have here an expression 
of the tendency to the repetition of an act. It is only after 



The Sense of Sight: Brightness Vision 107 

an animal acquires considerable familiarity with a situation 
that it begins to vary its behavior in accordance with rela- 
tively unimportant factors in the situation. It is this fact, 
illustrations of which may be seen in human life, as well as 
throughout the realm of animal behavior, that renders it im- 
perative that an animal be thoroughly acquainted with the 
apparatus for experimentation and with the experimenter 
before regular experiments are begun. Any animal will do 
things under most experimental conditions, but to discover 
the nature and scope of its ability it is necessary to make 
it thoroughly at home in the experimental situation. As 
the dancer began to feel at home in the visual discrimination 
apparatus it began to exercise its discriminating ability, the 
first form of which was choice according to position* 

Since there appears to be a slight preference on the part 
of most dancers for the black box in comparison with the 
white box, white-black training tests were given to fifty mice, 
and black-white to only four. The tests with each indi- 
vidual were continued until it had chosen correctly in all of 
the tests of three successive series (thirty tests). As the re- 
production of all the record sheets of these experiments 
would fill hundreds of pages and would provide most readers 
with little more information than is obtainable from a simple 
statement of the number of right and wrong choices, only 
the brightness discrimination records of Tables 6 and 7 are 
given in full. 

As a basis for the comparison of the results of* the white- 
black tests with those of the black-white tests, two represent- 
ative sets of data for each of these conditions of brightness 
discrimination are presented (Tables 9 and 10). In these 
tables only the number of right and wrong choices for each 
series of ten tests appears. 

Tables 9 and 10 indicate — if we grant that the precautionary 



io8 



The Dancing Mouse 



TABLE 9 
White-Black Tests 









No. 210 


No. 215 




Date 


Age, 28 Days 


Age, 28 Days 


Series 














Right 


Wrong 


Right 


Wrong 






(White) 


(Black) 


(White) 


(Black) 


A 


June 22 


4 


6 


2 


8 


B 


23 


4 


6 


2 


8 


I 


24 


4 


6 


3 


7 


2 


25 


6 


4 


5 


5 


3 


26 


7 


3 


7 


3 


4 


27 


5 


5 


8 


2 


5 


28 


7 


3 


9 


I 


6 


29 


8 


2 


8 


2 


7 


30 


9 


I 


9 


I 


8 


July I 


10 





10 





9 


2 


10 





9 


I 


lO 


3 


10 





10 





II 


4 


— 


— 


10 





12 


5 


— 


— 


10 






tests to be described later exclude the possibility of other 
forms of discrimination — that the dancer is able to tell white 
from black; that it is somewhat easier, as the preference 
tests might lead us to expect, for it to learn to go to the black 
than to the white, and that the male forms the habit of choos- 
ing on the basis of brightness discrimination more quickly 
than the female. 

It is now necessary to justify the interpretation of these 
results as evidence of brightness discrimination by proving 
that all other conditions for choice except brightness dif- 
ference may be excluded without interfering with the ani- 
mal's ability to select the right box. We shall consider in 



The Sense of Sight: Brightness Vision 109 



TABLE 10 
Black-White Tests 







No 
Age, 3 


14 

2 Days 


No. 13 
Age, 32 Days 


Series 


Date 


Right 


Wrong 


Right 


Wrong 






(Black) 


(White) 


(Black) 


(White) 


I 


May 13* 


5 


5 


7 


3 


2 


14 


8 


2 


6 


4 


3 


15 


7 


3 


9 


I 


4 


16 


9 


I 


9 


I 


5 


17 


10 





10 





6 


18 


10 





9 


I 


7 


19 


10 





10 





8 


20 


— 


— 


10 





9 


21 


— 


— 


10 


-o 



order the possibility of discrimination by position, by odor, 
and by texture and form of the cardboards. 

The tendency which the dancer has in common with many, 
if not all, animals to perform the same movement or follow 
the same path under uniform conditions is an important 
source of error in many habit-formation experiments. This 
tendency is evident even from casual observation of the be- 
havior of the dancer. The ease with which the habit of 
choosing the box on the left or the box on the right is formed 
in comparison with that of choosing the white box or the 
black box is strikingly shown by the following experiment. 
Five mice were given one series of ten trials each in the dis- 
crimination box of Figure 14 without the presence of card- 
boards or of other means of visual discrimination. The 
electric shock was given whenever the box on the left was 
entered. Thus without other guidance than that of direc- 
^ No preference tests were given. 



no 



The Dancing Mouse 



tion, for the boxes themselves were interchanged in posi- 
tion, and, as was proved by additional tests, the animals were 
utterly unable to tell one from the other, the mouse was re- 
quired to choose the box on its right. Only one of the five 
animals went to the box on the left after once experiencing the 
electric shock. The results of the series are given in Table ii. 

TABLE II 
Choice by Position 





Choices of 
Box ON Right 


Choices of 
Box ON Left 


First mouse 

Second mouse 

Third mouse ....... 

Fourth mouse . 

Fifth mouse 


9 
8 

9 
9 
9 


I 
2 

I 
I 
I 



This conclusively proves that the habit of turning in a 
certain direction or of choosing by position can be formed 
more readily than a habit which depends upon visual dis- 
crimination. A rough comparison justifies the statement 
that it takes from six to ten times as long for the dancer to 
learn to choose the white box as it does to learn to choose 
the box on the right. Since this is true, it is exceedingly im- 
portant that the possibility of choice by position or direction 
of movement be excluded in the case of tests of brightness 
discrimination. To indicate how this was eft'ectively ac- 
complished in the experiments, the changes in the position of 
the cardboards made in the case of a standard set of white- 
black series are shown in Table 12. The number of the 
series, beginning at the top of the table with the two lettered 
preference series, is given in the first column at the left, the 
number of the tests at the top of the table, and the posi- 
tion of the white cardboard, left or right, is indicated below 
by the letters / (left) and r (right). 



The Sense of Sight : Brightness Vision 1 1 



TABLE 12 
Position of White Cardboards for a Set of 150 Tests 



Series 


^ 


2 


3 


4 


5 


6 


7 


8 


9 


10 


Preference 






















A 


1 




1 










r 


I 




B 






r 










1 






I 






r 
















2 






r 
















3 






1 
















4 






1 










r 






5 






r 
















6 






r 










r 


^ 




7 






1 
















8 






1 
















9 






r 
















10 






1 
















II 






r 
















12 






r 
















13 






r 










r 






14 






1 










r 


I 


r 


15 






r 










1 


r 


1 



It is to be noted that in the case of each series of ten tests 
the white cardboard was on the left five times and on the 
right five times. Thus the establishment of a tendency in 
favor of one side was avoided. The irregularity of the 
changes in position rendered it impossible for the mouse to 
depend upon position in its choice. It is an interesting fact 
that the dancer quickly learns to choose correctly by posi- 
tion if the cardboards are alternately on the left box and on 
the right. 

The prevalent, although ill-founded, impression that mice 
have an exceedingly keen sense of smell might lead a critic 
of these experiments to claim that discrimination in all prob- 



112 The Dancing Mouse 

ability was olfactory rather than visual. As precautions 
against this possibility the cardboards were renewed fre- 
quently, so that no odor from the body of the mouse itself 
should serve as a guiding condition, different kinds of card- 
board were used from time to time, and, as a final test, the 
cardboards were coated with shellac so that whatever charac- 
teristic odor they may have had for the dancer was dis- 
guised if not totally destroyed. Despite all these precautions 
the discrimination of the boxes continued. A still more con- 
clusive proof that we have to do with brightness discrimina- 
tion, and that alone, in these experiments is furnished by the 
results of white-black tests made with an apparatus which 
was so arranged that light was transmitted into the two 
electric- boxes through a ground glass .plate in the end of 
each box. No cardboards were used. The illumination of 
each box was controlled by changes in the position of the 
sources of light. Under these conditions, so far as could be 
ascertained by critical examination of the results, in addition 
to careful observation of the behavior of the animals as they 
made their choices, there was no other guiding factor than 
brightness difference. Nevertheless the mice discriminated 
the white from the black perfectly. This renders unneces- 
sary any discussion of the possibility of discrimination by 
the texture or form of the cardboards. 

Since a variety of precautionary tests failed to reveal the 
presence, in these experiments, of any condition other than 
brightness difference by which the mice were enabled to 
choose correctly, and since evidence of ability to discriminate 
brightness differences was obtained by the use of both re- 
flected light (cardboards) and transmitted light (lamps 
behind ground glass), it is necessary to conclude that the 
dancer possesses brightness vision. 



CHAPTER VIII 
The Sense of Sight : Brightness Vision {Continued) 

Since the ability of the dancer to perceive brightness has 
been demonstrated by the experiments of the previous chap- 
ter, the next step in this investigation of the nature of vision 
is a study of the dehcacy of brightness discrimination, and 
of the relation of the just perceivable difference to brightness 
value. Expressed in another way, the problems of this por- 
tion of the investigation are to determine how slight a dif- 
ference in brightness enables the dancer to discriminate one 
light from another, and what is the relation between the 
absolute brightnesses of two lights and that amount of dif- 
ference which is just sufficient to render the lights distin- 
guishable. It has been discovered in the case of the human 
being that a stimulus must be increased by a certain definite 
fraction of its own value if it is to seem different. For 
brightness, within certain intensity limits, this increase must 
be about one one-hundredth ; a brightness of loo units, for 
example, is just perceivably different from one of loi units. 
The formulation of this relation between the amount of a 
stimulus and the amount of change which is necessary that 
a difference be noted is known as Weber's law. Does this 
law, in any form, hold for the brightness vision of the danc- 
ing mouse? 

Two methods were used in the study of these problems. For 
the first problem, that of the delicacy of brightness discrimina- 
tion, I first used light which was reflected from gray papers, 
according to the method of Chapter VII. For the second, 
I 113 



114 The Dancing Mouse 

the Weber's law test, transmitted light was used, in an ap- 
paratus which will be described later. Either of these meth- 
ods might have been used for the solution of both problems. 
Which of them is the more satisfactory is definitely decided 
by the results which make up the material of this chapter^ 
Under natural conditions the dancer probably sees objects 
which reflect light more frequently than it does those which 
transmit it; it would seem fairer, therefore, to require it to 
discriminate surfaces which differ in brightness. This the 
use of gray papers does. But, on the other hand, gray papers 
are open to the objections that they nay not be entirely 
colorless (neutral), and that their brightness values cannot 
be changed readily by the experimenter. As will be made 
clear in the subsequent description of the experiments with 
transmitted light, neither of these objections can be raised 
in connection with the second method of experimentation. 

To determine the delicacy of discrimination with reflected 
light it is necessary to have a series of neutral grays (colorless) 
whose adjacent members differ from one another in bright- 
ness by less than the threshold of discrimination of the animal 
to be tested. A series which promised to fulfill these con- 
ditions was that of Richard Nendel of Berlin. It consists 
of fifty papers, beginning with pure white, numbered i, and 
passing by almost imperceptible steps of decrease in bright- 
ness through the grays to black, which is numbered 50. For 
the present we may assume that these papers are so nearly 
neutral that whatever discrimination occurs is due to bright- 
ness. The differences between successive papers of the series 
are perceptible to man. The question is, can they, under 
favorable conditions of illumination, be perceived by the 
dancer ? 

On the basis of the fact that the dancer can discriminate 
between white and black, two grays which differed from one 



The Sense of Sight : Brightness Vision 115 

another in brightness by a considerable amount were chosen 
from the Nendel series; these were numbers 10 and 20. It 
seemed certain, from the results of previous experiments, that 
the discrimination of these papers by brightness difference 
would be possible, and that therefore the use of papers be- 
tween these two extremes would suffice to demonstrate the 




Figure i6. Three of Nendel's gray papers: Nos. lo, 15, and 20. To exhibit 
diflferences in brightness. 

dehcacy of discrimination. In Figure i6 we have a fairly 
accurate representation of the relative brightness of the 
Nendel papers Nos. lo, 15, and 20. 

Pieces of the gray papers were pasted upon cardboard 
carriers so that they might be placed in the discrimination box 
as were the white and black cardboards in the tests of bright- 
ness vision previously described. Mice which had been 
trained to choose the white box by series of white-black tests 
were now tested with light gray (No. 10) and dark gray 
(No. 20), my assumption being that they would immediately 



ii6 The Dancing Mouse 

choose the brighter of the two if they were able to detect 
the difference. As a matter of fact this did not always occur ; 
some individuals had to be trained to discriminate gray No. lo 
from gray No. 20. As soon as an individual had been so 
trained that the ability to choose the lighter of these grays was 
perfect, it was tested with No. 10 in combination with No. 15. 
If these in turn proved to be discriminable, No. 10 could be 
used with No. 14, with No. 13, and so on until either the hmit 
of discrimination or that of the series had been reached. 

That it was not necessary to use other combinations than 
10 with 20, and 10 with 15 is demonstrated by the results 
of Table 13. Mouse No. 420, whose behavior was not essen- 
tially different from that of three other individuals which 
were tested for gray discrimination, learned with difficulty 
to choose gray No. 10 even when it was used with No. 20. 
Two series of ten tests each were given to this mouse daily, 
and not until the twentieth of these series (200 tests) did he 
succeed in making ten correct choices in succession. Imme- 
diately after this series of correct choices, tests with grays 
No. 10 and No. 15 were begun. In the case of this amount 
of brightness difference twenty series failed to reveal discrimi- 
nation. The average number of right choices in the series 
is slightly in excess of the mistakes, 5.8 as compared with 4.2. 

From the experiments with gray papers we may conclude 
that under the conditions of the tests the amount by which 
Nendel's gray No. 10 differs in brightness from No. 20 is near 
the threshold of discrimination, or, in other words, that the 
difference in the brightness of the adjacent grays of Figure 16 
is scarcely sufficient to enable the dancer to distinguish them. 

This result of the tests with gray papers surprised me very 
much at the time of the experiments, for all my previous ob- 
servation of the dancer had led me to believe that it is very 
sensitive to light. It was only after a long series of tests with 



The Sense of Sight : Brightness Vision 117 



TABLE 13 

Gray Discrimination 

The Delicacy of Brightness Discrimination 

No. 420 







Grays Nos. io 




Grays Nos. io 






AND 20 




AND 15 


Series 






Date 






No. 10 


No. 20 




No. 10 


No. IS 






(Right) 


(Wrong) 




(Right) 


(Wrong) 


I 


Jan. 26 


5 


5 


Feb. 6 


8 


2 


2 


27 


8 


2 


6 


5 


5 


3 


28 


6 


4 


7 


9 


I 


4 


28 


2 


8 


7 


7 


3 


5 


29 


I 


9 


8 


5 


5 


6 


29 


6 


4 


8 


6 


4 


7 


30 


9 


I 


9 


5 


5 


8 


30 


7 


3 


9 


6 


4 


9 


31 


6 


4 


10 


8 


2 


10 


31 


4 


6 


10 


3 


7 


II 


Feb. I 


7 


3 


II 


4 


6 


12 


I 


8 


2 


II 


4 


6 


13 


2 


7 


3 


12 


7 


3 


14 


2 


8 


2 


12 


7 


3 


15 


3 


9 


I 


13 


6 


4 


16 


3 


9 


I 


13 


4 


6 


17 


4 


6 


4 


14 


4 


6 


18 


4 


9 


I 


14 


5 


5 


19 


5 


6 


4 


15 


5 


5 


20 


5 


10 





15 


8 


2 


Averages 


6.6 


3-4 




5.8 


4.2 



transmitted light, in what is now to be described as the Weber's 
law apparatus, that I was able to account for the meager power 
of discrimination which the mice exhibited in the gray tests. 
As it happened, the Weber's law experiment contributed quite 



ii8 The Dancing Mouse 

as importantly to the solution of our first problem as to 
that of the second, for which it was especially planned. 

For the Weber's law experiment a box similar to that used 
in the previous brightness discrimination experiments (Figure 
14) was so arranged that its two electric-boxes could be 
illuminated independently by the light from incandescent 
lamps directly above them. The arrangements of the light- 
box and the lamps, as well as their relations to the other im- 
portant parts of the apparatus, are shown in Figure 17. The 
light-box consisted of two compartments, of which one may 
be considered as the upward extension of the left electric- 
box and the other of the right electric-box. The light-box 
was pivoted at A and could be turned through an angle of 
180° by the experimenter. Thus, by the turning of the light- 
box, the lamp which in the case of one test illuminated the 
left electric- box could be brought into such a position that in 
the case of the next test it illuminated the right electric-box. 
The practical convenience of this will be appreciated when 
the number of times that the brightnesses of the two boxes 
had to be reversed is considered. The light-box was left open 
at the top for ventilation and the prevention of any consider- 
able increase in the temperature of the experiment box. In 
one side of each of the compartments of the light-box a slit 
(5, B of the figure) was cut out for an incandescent lamp 
holder. A strip of leatherette, fitted closely into inch grooves 
at the edges of the slit, prevented light from escaping through 
these openings in the sides of the light-box. By moving the 
strips of leatherette, one of which appears in the figure, C, the 
lamps could be changed in position with reference to the bottom 
of the electric- box. A scale, 5, at the edge of each slit enabled 
the experimenter to determine the distance of the lamp from 
the floor of the electric-box. The front of the light-box was 
closed, instead of being open as it appears in the figure. 



The Sense of Sight : Brightness Vision 119 




Figure 17. — Weber's law apparatus for testing brightness discrimination. 
Lower part, discrimination box similar to that of Figure 14. Upper part, rotatory 
light-box, pivoted at -4, and divided into two compartments by a partition P in 
the middle. L, L, incandescent lamps movable in slits, B, B, in which a narrow 
strip of leatherette, C, serves to prevent the escape of light. S, scale. 



I20 The Dancing Mouse 

This apparatus has the following advantages. First, the 
electric-boxes, between which the mouse is expected to dis- 
criminate by means of their difference in brightness, are 
illuminated from above and the light therefore does not shine 
directly from the lamps into the eyes of the animal, as it 
approaches the entrances to the boxes. Choice is required, 
therefore, between illuminated spaces instead of between 
two directly illuminated surfaces. Second, the amount of 
illumination of each electric-box can be accurately measured 
by the use of a photometer. Third, since the same kind of 
lamp is used in each box, and further, since the lamps may 
be interchanged at any time, discrimination by qualitative 
instead of quantitative difTerence in illumination is excluded. 
And finally, fourth, the tests can be made expeditiously, 
conveniently, and under such simple conditions that there 
should be no considerable error of measurement or of ob- 
servation within the range of brightness which must be used. 

It was my purpose in the experiment with this apparatus 
to ascertain how great the diflference in the illumination of the 
two electric-boxes must be in order that the mouse should 
be able to choose the brighter of them. This I attempted 
to do by fixing an incandescent lamp of a certain known 
illuminating power at such a position in one compartment of 
the light-box that the electric-box below it was illuminated 
by what I call a standard value, and by moving the incandes- 
cent lamp in the other compartment of the light-box until 
the illumination of the electric-box below it was just suffi- 
ciently less than that of the standard to enable the dancer 
to distinguish them, and thereby to choose the brighter one. 
The light which was changed from series to series I shall call the 
variable, in contrast with the standard, which was unchanged. 

The tests, which were made in a dark-room under uni- 
form conditions, were given in series of fifty each ; usually 



The Sense of Sight: Brightness Vision 121 

only one such series was given per day, but sometimes one was 
given in the morning and another in the afternoon of the 
same day. To prevent choice by position the Hghts were re- 
versed in position irregularly, first one, then the other, illu- 
minating the right electric-box. For the fifty tests of each 
initial series the order of the changes in position was as 
follows: standard (brighter light) on the / (left), /, r (right), 
r, I, /, r, r, I, r, I, r, I, I, r, r, I, I, r, r, /, /, /, r, r, r, I, r, I, r, r, 
r, /, /, /, r, r, r, I, I, r, I, r, I, r, I, r, I, r, I. Twenty- five times in 
fifty the standard light illuminated the right electric- box, and 
the same number of times it illuminated the left electric- box. 
When a second series was given under the same conditions 
of illumination, a different order of change was followed. 

In order to discover whether Weber's law holds in the case 
of the brightness vision of the dancer it was necessary for me 
to determine the just perceivable difference between the stan- 
dard and the variable lights for two or more standard values. 
I chose to work with three values, 5, 20, and 80 hefners, and 
I was able to discover with a fair degree of accuracy how much 
less than 5, 20, or 80 hefners, as the case might be, the vari- 
able light had to be in order that it should be discriminable 
from the other. For the work with the 5 hefner standard 
I used 2-candle-power lamps,^ for the 20, 4-candle-power, 
and for the 80, i6-candle- power. 

^ I give merely the commercial markings of the lamps. They had been 
photomctered carefully by two observers by means of a Lummer-Brodhun 
photometer and a Hefner amyl acetate lamp previous to their use in the 
experiment. For the photometric measurements in connection with the 
Weber's law tests I made use of the Hefner lamp with the hope of attain- 
ing greater accuracy than had been possible with a standard paraffine candle, 
in the case of measurements which I had made in connection with the 
experiments on color vision that are reported in Chapters IX and X. The 
Hefner unit is the amount of light produced by an amyl acetate lamp at a 
flame height of 40 mm. ^See Stine's " Photometrical Measurements.") A 
paraffine candle at a flame height of 50 mm. is equal to 1.2 Hefner units. 



122 The Dancing Mouse 

For reasons which will soon appear, Weber's law tests 
were made with only one dancer. This individual, No. 51, 
had been thoroughly trained in white-black discrimination 
previous to the experiments in the apparatus which is repre- 
sented in Figure 17. Having given No. 51 more than two 
hundred preliminary tests in the Weber's law apparatus with 
the electric -boxes sufficiently different in brightness to enable 
her to discriminate readily, I began my experiments by trying 
to ascertain how much less the value of the illumination ot 
one electric-box must be in order that it should be discrim- 
inable from a value of 20 hefners in the other electric-box. 
In recording the several series of tests and their results here- 
after, I shall state in Hefner units the value of the fixed or 
standard light and the value of the variable light, the difference 
between the two in terms of the former, and the average 
number of wrong choices in per cent. 

With the lamps so placed that the difference in the illumi- 
nation of the two electric-boxes was .53 of the value of the 
standard, that is about one half. No. 51 made twenty wrong 
choices in one hundred, or 20 per cent. When the difference 
was reduced to .36 (one third) the number of errors increased 
to 36 per cent, and with an intermediate difference of .48 
there were 26 per cent of errors (see Table 14). 

Are these results indicative of discrimination, or are the 
errors in choice too numerous to justify the statement that 
the dancer was able to distinguish the boxes by their differ- 
ence in brightness? Evidently this question cannot be 
answered satisfactorily until we have decided what the per- 
centage of correct choices should be in order that it be ac- 
cepted as evidence of ability to discriminate, or, to put it in 
terms of errors, what percentage of wrong choices is indica- 
tive of the point of just perceivable difference in brightness. 
Theoretically, there should be as many mistakes as right 



r 



The Sense of Sight : Brightness Vision 123 



choices, 50 per cent of each, when the two electric-boxes are 
equally illuminated (indiscriminable), but in practice this 
does not prove to be the case because the dancer tends to 
return to that electric-box through which in the previous 
test it passed safely, whereas it does not tend in similar fash- 
ion to reenter the box in which it has just received an elec- 
tric shock. The result is that the percentage of right choices, 
especially in the case of series which have the right box in 
the same position two, three, or four times in succession, 
rises as high as 60 or 70, even when the visual conditions 
are indiscriminable. Abundant evidence in support of this 
statement is presented in Chapters VII and IX, but at 
this point I may further call attention to the results of an 
experiment in the Weber's law apparatus which was made 
especially to test the matter. The results appear under the 
date of May 27 in Table 14. In this experiment, despite 
the fact that both boxes were illuminated by 80 hefners, the 
mouse chose the standard (the illumination in which it was 
not shocked) 59 times in 100. In other words the percentage 
of error was 41 instead of 50. It is evident, therefore, that 
as low a percentage of errors as 40 is not necessarily indicative 
of discrimination. Anything below 40 per cent is likelyy 
however, to be the result of ability to distinguish the brighter 
from the darker box. To be on the safe side we may agree 
to consider 25 wrong choices per 100 as indicative of a just 
perceivable difference in illumination. Fewer mistakes we 
shall consider indicative of a difference in illumination which 
is readily perceivable, and more as indicative of a difference 
which the mouse cannot detect. The reader will bear in mind 
as he examines Table 14 that 25 per cent of wrong choices 
indicates the point of just perceivable difference in brightness. 
If we apply this rule to the results of the first tests, reported 
above, it appears that a standard of 20 hefners was distin- 



124 The Dancing Mouse 

TABLE 14 

Results of Weber's Law Experiments 

Brightness vision 



Date 


Number 
OF Tests 


Standard 
Light 


Variable 
Light 


Difference 


% OF Errors 


May 13 


100 


20 


9.4 


•53 


20 


15 


100 


20 


12.8 


.36 


36 


16 


100 


20 


10.8 


.46 


26 


20 


50 


80 


37-6 


•53 


6 


21 


50 


80 


51.3 


.36 


10 


22 


100 


80 


71. 1 


.11 


35 


24 


100 


80 


60.0 


•25 


21 


25 


100 


80 


65.0 


.19 


25 


27 


100 


80 


80 





41 


28 


50 


5 


2-5 


•50 


18 


29 


50 


5 


4.0 


.20 


14 


29 


100 


5 


4-5 


.10 


25 


31 


50 


5 


4.25 


•15 


20 


June I 


50 


5 


4-85 


.03 


.48 


2 


50 


20 


15.0 


•25 


16 


3 


50 


20 


17.4 


.13 


22 


3 


100 


20 


18.0 


.10 


22 


4 


100 


80 


72.0 


.10 


18 


5 


100 


5 


4-5 


.10 


12 


7 


100 


5 


4.67 


.067 


46 


8 


50 


80 


74.67 


.067 


56 


9 


50 


20 


18.67 


.067 


44 



guished from a variable of 9.4 hefners (.53 difference), for 
the percentage of errors v^as only 20. But in the case of a 
difference of .36 in the illuminations lack of discrimination 
is indicated by 36 per cent of errors. A difference of .46 
gave a frequency of error so close to the required 25 (26 per 
cent) that I accepted the result as a satisfactory determination 
of the just perceivable difference for the 20 hefner standard 
and proceeded to experiment with another standard value. 



The Sense of Sight: Brightness Vision 125 

The results which were obtained in the case of this second 
standard, the value of which was 80 hefners, are strikingly 
different from those for the 20 hefner standard. Naturally 
I began the tests with this new standard by making the dif- 
ferences the same as those for which determinations had been 
made in the case of the 20 standard. Much to my surprise 
only 6 per cent of errors resulted when the difference in illumi- 
nation was .53. I finally discovered that about .19 difference 
(about one fifth) could be discriminated with that degree of 
accuracy which is indicated by 25 per cent of mistakes. 

So far as I could judge from the results of determinations 
for the 20 and the 80 hefner standards, Weber's law does 
not hold for the dancer. With the former a difference of 
almost one half was necessary for discrimination; with the 
latter a difference of about one fifth could be perceived. But 
before presenting additional results I should explain the con- 
struction of Table 14, and comment upon the number of 
experiments which constitutes a set. 

The table contains the condensed results of several weeks 
of difficult experimentation. From left to right the columns, 
give the date of the initial series of a given set of experiments, 
the number of experiments in the set, the value of the standard 
Hght in hefners, the value of the variable light, the difference 
between the lights in terms of the standard (the variable was 
always less than the standard), and the percentage of errors 
or wrong choices. Very early in the investigation I discovered 
that one hundred tests with any given values of the lights 
sufficed to reveal whatever discriminating ability the mouse 
possessed at the time. In some instances either the presence 
or the lack of discrimination was so clear, as the result of 50 
tests (first series), that the second series of 50 was not given. 
Consequently in the table the number of tests for the vari- 
ous values of the lights is sometimes 100, sometimes 50. 



126 The Dancing Mouse 

After finishing the experiments with the 80 standard on 
May 27 (see table) I decided, in spite of the evidence against 
Weber's law, to make tests with 5 as the standard, for it 
seemed not impossible that the lights were too bright for the 
dancer to discriminate readily. I even suspected that I 
might have been working outside of the brightness limits 
in which Weber's law holds, if it holds at all. The tests 
soon showed that a difference of one tenth made dis- 
crimination possible in the case of this standard. If the 
reader will examine the data of the table, he will note that a 
difference of .20 gave 14 per cent of mistakes; a difference 
of .03, 48 per cent. Evidently the former difference is above 
the threshold, the latter below it. But what of the interpreta- 
tion of the results in terms of Weber's law ? The difference 
instead of being one half or one fifth, as it was in the cases of 
the 20 and 80 standards respectively, has now become one 
tenth. Another surprise and another contradiction ! 

Had these three differences either increased or decreased 
regularly with the value of the standard I should have sus- 
pected that they indicated a principle or relationship which is 
different from but no less interesting than that which Weber's 
law expresses. But instead of reading 5 standard, difference 
one tenth; 20 standard, difference one fifth; 80 standard, 
difference one half: or 5 standard, difference one half; 20 
standard, difference one fifth; 80 standard, difference one 
tenth : they read 5 standard , difference one tenth ; 20 stand- 
ard, difference one half; 80 standard, difference one fifth. 
What does this mean ? I could think of no other explanation 
than that of the influence of training. It seemed not impos- 
sible, although not probable, that the mouse had been im- 
proving in ability to discriminate day by day. It is true that 
this in itself would be quite as interesting a fact as any 
which the experiment might reveal. 



The Sense of Sight: Brightness Vision 127 

To test the value of my supposition, I made additional 
experiments with the 20 standard, the results of which ap- 
pear under the dates June 2 and 3 of the table. These re- 
sults indicate quite definitely that the animal had been, and 
still was, improving in her abihty to discriminate. For in- 
stead of requiring a difference of about one half in order that 
she might distinguish the 20 standard from the variable 
light she was now able to discriminate with only 22 per cent 
of errors when the difference was one tenth. 

As it seemed most improbable that improvement by train- 
ing should continue much longer, I next gave additional tests 
with the 80 standard. Again a difference of one tenth was 
sufficient for accurate discrimination (18 per cent of errors). 
These series were followed immediately by further tests 
with the 5 standard. As the results indicated greater ease 
of discrimination with a difference of one tenth in the case 
of this standard than in the case of either of the others I was 
at first uncertain whether the results which I have tabulated 
under the dates June 3, 4, and 5 of the table should be in- 
terpreted in terms of Weber's law. 

Up to this point the experiments had definitely established 
two facts : that the dancer's ability to discriminate by means 
of brightness differences improves with training for a much 
longer period and to a far greater extent than I had supposed 
it would ; and that a difference of one tenth is sufficient 
to enable the animal to distinguish two lights in the case of 
the three standard values, 5, 20, and 80 hefners. The ques- 
tion remains, is this satisfactory evidence that Weber's law 
holds with respect to the brightness vision of the dancer, or 
do the results indicate rather, that this difference is more 
readily detected in the case of 5 as a standard (12 per cent 
error) than in the case of 20 as a standard (22 per cent 
error) ? 



128 The Danciiig Mouse 

For the purpose of settling this point I made tests for each 
of the three standards with a difference of only one fifteenth. 
In no instance did I obtain the least evidence of ability to 
discriminate. These final tests, in addition to establishing 
the fact that the limit of discrimination for No. 51, after she 
had been subjected to about two thousand tests, lay between 
one tenth and one fifteenth, proved to my satisfaction, when 
taken in connection with the results already discussed, that 
Weber's law does hold for the brightness vision of the dancer. 

In concluding this discussion of the Weber's law experi- 
ment I wish to call attention to the chief facts which have 
been revealed, and to make a critical comment. In my 
opinion it is extremely important that the student of animal 
behavior should note the fact that the dancer with which 
I worked week after week in the Weber's law investigation 
gradually improved in her ability to discriminate on the 
basis of brightness differences until she was able to distin- 
guish from one another two boxes whose difference in illu- 
mination was less than one tenth ^ that of the brighter 
box. At the beginning of the experiments a difference of one 
half did not enable her to choose as certainly as did a differ- 
ence of one tenth after she had chosen several hundred times- 
Evidently we are prone to underestimate the educability of 
our animal subjects. 

The reason that the experiments were carried out with 
only one mouse must now be apparent. It was a matter of 
time. The reader must not suppose that my study of this 
subject is completed. It is merely well begun, and I report it 
here in its unfinished state for the sake of the value of the 
method which I have worked out, rather than for the purpose of 
presenting the definite results which I obtained with No. 51. 

^ Under the conditions of the experiment I was unable to distinguish the 
electric -boxes when they differed by less than one twentieth. 



I 



The Sense of Sight : Brightness Vision 129 



The critical comment which I wish to make for the benefit 
of those who are working on similar problems is this. The 
phosphor bronze wires, on the bottom of the electric-boxes, 
by means of which an electric shock could be given to the 
mouse when it chose the wrong box, are needless sources of 
variability in the illumination of the boxes. They reflect the 
light into the eyes of the mouse too strongly, and unless they 
are kept perfectly clean and bright, serious inequahties of 
illumination appear. To avoid these undesirable conditions 
I propose hereafter to use a box within a box, so that the wires 
shall be hidden from the view of the animal as it attempts 
to discriminate. 

A brief description of the behavior of the dancer in the 
brightness discrimination experiments which have been de- 
scribed may very appropriately form the closing section of 
this chapter. For the experimenter, the incessant activity and 
inexhaustible energy of the animal are a never-failing source 
of interest and surprise. When a dancer is inactive in the 
experiment box, it is a good indication either of indisposition 
or of too low a temperature in the room. In no animal with 
which I am famihar is activity so much an end in itself as 
in this odd species of mouse. With striking facility most 
of the mice learn to open the wire swing doors from either 
side. They push them open with their noses in the direc- 
tion in which they were intended by the experimenter to 
work, and with almost equal ease they pull them open with 
their teeth in the direction in which they were not intended 
to work. In the rapidity with which this trick is learned, 
there are very noticeable individual differences. The pulling 
of these doors furnished an excellent opportunity for the study 
of the imitative tendency. 

When confronted with the two entrances of the electric- 
boxes, the dancer manifested at first only the hesitation caused 



130 The Dancing Mouse 

by being in a strange place. It did not seem much afraid, 
and usually did not hesitate long before entering one of the 
boxes. The first choice often determined the majority of 
the choices of the preference series. If the mouse happened 
to enter the left box, it kept on doing so until, having become 
so accustomed to its surroundings that it could take time from 
its strenuous running from A by way of the left box to the 
alley and thence to ^, to examine things in ^ a little, it ob- 
served the other entrance and in a seemingly half-curious, 
half- venturesome way entered it. In the case of other in- 
dividuals, he cardboards themselves seemed to determine the 
choices from the first. 

The electric shock, as punishment for entering the wrong 
box, came as a surprise. At times an individual would per- 
sistently attempt to enter, or even enter and retreat from the 
wrong box repeatedly, in spite of the shock. This may have 
been due in some instances to the effects of fright, but in 
others it certainly was due to the strength of the tendency to 
follow the course which had been taken most often previously. 
The next effect of the shock was to cause the animal to hesitate 
before the entrances to the boxes, to run from one to the other, 
poking its head into each and peering about cautiously, 
touching the cardboards at the entrances, apparently smelling 
of them, and in every way attempting to determine which 
box could be entered safely. I have at times seen a mouse 
run from one entrance to the other twenty times before mak- 
ing its choice ; now and then it would start to enter one and, 
when halfway in, draw back as if it had been shocked. Pos- 
sibly merely touching the wires with its fore paws was respon- 
sible for this simulation of a reaction to the shock. The 
gradual waning of this inhibition of the forward movement 
was one of the most interesting features of the experiment. 
Could we but discover what the psychical states and the 



The Sense of Sight : Brightness Vision 1 3 1 

physiological conditions of the animal were during this pe- 
riod of choosing, comparative psychology and physiology 
would advance by a bound. 

If the conditions at the entrances of the two boxes were 
discriminable, the mouse usually learned within one hundred 
experiences to choose the right box without much hesitation. 
Three distinct methods of choice were exhibited by different 
individuals, and to a certain extent by the same individual 
from time to time. These methods, which I have desig- 
nated choice hy affirmation, choice by negation, and choice by 
comparison, are of peculiar interest to the psychologist and 
logician. 

When an individual runs directly to the entrance of the 
right box, and, after stopping for an instant to examine it, 
enters, the choice may be described as recognition of the 
right box. I call it choice by affirmation because the act of 
the animal is equivalent to the judgment — '' this is it." If in- 
stead it runs directly to the wrong box, and, after examining it, 
turns to the other box and enters without pause for examina- 
tion, its behavior may be described as recognition of the wrong 
box. This I call choice by negation because the act seems 
equivalent to the judgment — ''this is not it." Further, it 
seems to imply the judgment — " therefore the other is it." In 
the Hght of this fact, this type of choice might appropriately 
be called choice by exclusion. Finally, when the mouse runs 
first to one box and then to the other, and repeats this any- 
where from one to fifty times, the choice may be described as 
comparison of the boxes; therefore, I call it choice by com- 
parison. Certain individuals choose first by comparison, 
and later almost uniformly by affirmation and negation. 
Whenever the conditions are difficult to discriminate, choice 
by comparison occurs most frequently and persistently. If, 
however, the conditions happen to be absolutely indiscrim- 



132 The Dancing Mouse 

inable, as was true, for example, in the case of the 'sound 
tests, in certain of the Weber's law tests, and in the plain 
electric-box tests, the period of hesitation rapidly increases 
during the first three or four series of tests, then the mouse 
seems to lessen its efforts to discriminate and more and more 
tends to rush into one of the boxes without hesitation or 
examination, and apparently with the expectation of a shock, 
but with the intention of getting it over as soon as possible. 
Now and then under such conditions there is a marked ten- 
dency to enter the same box each time. Indiscriminable 
conditions are likely to render the animals fearful of the ex- 
periment ; instead of going from ^ to ^ willingly, they fight 
against making the trip. They refuse to pass from A \.<d B\ 
and when in J5, they fight against being driven toward the 
entrances to the electric-boxes. 

In marked contrast with this behavior on the part of the 
mouse under conditions which do not permit it to choose 
correctly is that of the animal which has learned what is ex- 
pected of it. The latter, far from holding back or fighting 
against the conditions which urge it forward, is so eager to 
make the trip that it sometimes has to be forced to wait while 
the experimenter records the results of the tests. There is 
evidence of delight in the freedom of movement and in the 
variety of activity which the experiment furnishes. The 
thoroughly trained dancer runs into B almost as soon as it 
has been placed in A by the experimenter; it chooses the 
right entrance by one of the three methods described above, 
immediately, or after whirling about a few times in B; it 
runs through E and back to A as quickly as it can, and al- 
most before the experimenter has had time to record the 
result of the choice it is again in B ready for another choice. 



CHAPTER IX 

The Sense of Sight: Color Vision 

Is the dancing mouse able to discriminate colors as we 
do? Does it possess anything which may properly be 
called color vision? If so, what is the nature of its ability 
in this sense field ? Early in my study of the mice I attempted 
to answer these and similar questions, for the fact that they 
are completely deaf during the whole or the greater part of 
their lives suggested to me the query, are they otherwise 
defective in sense equipment? In the following account of 
my study of color vision, I shall describe the evolution of my 
methods in addition to stating the results which were obtained 
and the conclusions to which they led me. P'or in this case 
the development of a method of research is quite as interest- 
ing as the facts which the method in its various stages of 
evolution revealed. 

Observation of the behavior of the dancer under natural 
conditions caused me to suspect that it is either defective 
in color vision or possesses a sense which is very different 
from human vision. I therefore devised the following extremely 
simple method of testing the animal's ability to distinguish 
one color from another. In opposite corners of a wooden 
box 26 cm. long, 23 cm. wide, and 11 cm. deep, two tin boxes 
5 cm. in diameter and 1.5 cm. deep were placed, as is shown 
in part I of Figure 18. One of these boxes was covered on 
the outside with blue paper (B of Figure 18), and the other 
with orange ^ (O of Figure 18). A small quantity of "force" 

^ These were the Milton Bradley blue and orange papers. 
^33 



134 



The Dancing Mouse 



was placed in the orange box. As the purpose of the test was 
to discover whether the animals could learn to go directly 







\/ 



© » © 



N/ 




in IV 

Figure i8. — Food-box apparatus for color discrimination experiments. O, 
orange food-box; 5, blue food-box; i, 2, 3, 4, different positions of the food- 
boxes, O and B; I, II, III, IV, figures in which the arrows indicate the direction 
in which the food-boxes were moved. 

to the box which contained the food, the experiments were 
made each morning before the mice had been fed. The 
experimental procedure consisted in placing the individual 
to be tested in the end of the large wooden box opposite the 
color boxes, and then permitting it to run about exploring 



The Sense of Sight: Color Vision 135 



the box until it found the food in the orange box. While it 
was busily engaged in eating a piece of ''force" which it had 
taken from the box and 
was holding in its fore 
paws, squirrel fashion, 
the color boxes were 
quickly and without dis- 
turbance shifted in the 
directions indicated by 
the arrows of Figure 18, 

1. Consequently, when 
the animal was ready for 
another piece of "force," 
the food- box was in the 
corresponding corner of 
the opposite end of the 
experiment box (position 

2, 18, II). After the 
mouse had again suc- 

. r J. . 1 Figure 19. — Food-box apparatus with mov- 

Ceeded m hndmg it, the able partitions. O, orange food-box; 5, blue 

orange box was shifted food-box ;X, starting point for mouse ; ^, point 

. . ,. at which both food-boxes become visible to the 

in position as is indl- mouse as it approaches them; 1,2, two different 

Cated by the arrows in positions of the food-boxes; T, T, movable 

Figure 18, II. Thus the P^^^^'^^"^' (After Doctor Waugh.) 

tests were continued, the boxes being shifted after each 
success on the part of the animal in such a way that for no 
two successive tests was the position of the food-box the same ; 
it occupied successively the positions i, 2, 3, and 4 of the fig- 
ure, and then returned to i . Each series consisted of 20 tests. 
An improvement on this method, which was suggested 
by Doctor Karl Waugh, has been used by him in a study 
of the sense of vision in the common mouse. It consisted 
in the introduction, at the middle of the experiment box, of 




136 The Da7icing Mouse 

two wooden partitions which were pivoted on their mid- 
vertical axes so that they could be placed in either of the posi- 
tions indicated in Figure 19. Let us suppose that a mouse 
to be tested for color vision in this apparatus has been placed 
at X. In order to obtain food it must pass through A and 
choose either the orange or the blue box. If it chooses the 
former, the test is recorded as correct ; if it goes to the blue 
box first, and then to the orange, it is counted an error. While 
the animal is eating, the experimenter shifts the boxes to 
position I of Figure 19, and at the same time moves the par- 
titions so that they occupy the position indicated by the dotted 
lines. The chief advantage of this improvement in method 
is that the animal is forced to approach the color boxes from 
a point midway between them, instead of following the sides 
of the experiment box, as it is inclined to do, until it happens 
to come to the food-box. This renders the test fairer, 
for presumably the animal has an opportunity to see both 
boxes from A and can make its choice at that point of 
vantage. 

Two males, A and B, of whose age I am ignorant, were 
each given seventeen series of tests in the apparatus of 
Figure 18. A single series, consisting of twenty choices, 
was given daily. Whether the animal chose correctly or not, 
it was allowed to get food ; that is, if it went first to the blue 
box, thus furnishing the condition for a record of error, it 
was permitted to pass on to the orange box and take a piece 
of "force." No attempt was made to increase the animal's 
desire for food by starving it. Usually it sought the food -box 
eagerly; when it would not do so, the series was abandoned 
and work postponed. "Force" proved a very convenient 
form of food in these tests. The mice are fond of it, and they 
quickly learned to take a flake out of the box instead of trying 
to get into the box and sit there eating, for when they attempted 



The Sense of Sight: Color Vision 137 

the latter they were promptly pushed to one side by the ex- 
perimenter and the box, as well as the food, was removed to 
a new position. 

The results of the tests appear in Table 15. No record 
of the choices in the first two of the 17 series was kept. The 
totals therefore include 15 series, or 300 tests, with each 
individual. Neither the daily records nor the totals of this 
table demonstrate choice on the basis of color discrimination. 
Either the dancers were not able to tell one box from the 
other, or they did not learn to go directly to the orange box. 
It might be urged with reason that there is no sufficiently 
strong motive for the avoidance of an incorrect choice. A 
mistake simply means a moment's delay in finding food, and 
this is not so serious a matter as stopping to discriminate. 
I am inclined, in the light of result of other experiments, to 
believe that there is a great deal in this objection to the method. 
Reward for a correct choice should be supplemented by some 
form of punishment for a mistake. This conclusion was 
forced upon me by the results of these preliminary experiments 
on color vision and by my observation of the behavior of the 
animals in the apparatus. At the time the above tests were 
made I believed that I had demonstrated the inability of 
the dancer to distinguish orange from blue, but now, after 
two years' additional work on the subject, I beheve instead 
that the method was defective. 

The next step in the evolution of a method of testing the 
dancer's color vision was the construction of the apparatus 
(Figures 14 and 15) which was described in Chapter VII, 
p. 92. In connection with this experiment box the basis 
for a new motive was introduced, namely, the punishment 
of mistakes by an electric shock. Colored cardboards, in- 
stead of the white, black, or grays of the brightness tests, 
were placed in the electric-boxes. 



138 



The Dancing Mouse 



TABLE 15 
Orange-Blue Tests, with Food-Box 







Date 
1Q04 


Mouse A 


Mouse B 


Series 


Right 
(Orange) 


Wrong 
(Blue) 


Right 
(Orange) 


Wrong 
(Blue). 


I 
2 

3 
4 
5 
6 

7 
8 

9 
10 
II 
12 
13 
14 
15 
16 

17 


Dec. 6 

7 
8 

9 
10 
II 
12 
13 
14 
15 
16 

17 
18 

19 
20 
22 
23 


12 
10 

15 
10 

9 
10 

12 
13 
13 
12 
II 
13 
13 
14 
10 


8 
10 

5 

10 
II 
10 
8 
7 
7 
8 

9 
7 
7 
6 
10 


12 

9 
10 
12 

9 
9 
12 
12 
10 
10 
10 
8 

9 
12 

9 


8 
II 
10 

8 
II 
II 

8 

8 
10 
10 
10 
12 
II 

8 
II 


Totals 


177 


123 


153 


147 



In preliminary tests, at the rate of four per day, the colored 
cardboards were placed only at the entrances to the boxes, not 
inside, and as was true also in the case of brightness tests 
under like conditions, no evidence of discrimination was 
obtained from ten days' training. This seemed to indicate 
that a considerable area of the colored surface should be 
exposed to the mouse's view, if discrimination were to be 
made reasonably easy. 

This conclusion was supported by the results of other 
preliminary experiments in which rectangular pieces of colored 



The Sense of Sight: Color Vision 139 

papers/ 6 by 3 cm., were placed on the floor at the entrances 
to the electric-boxes, instead of on the walls of the boxes. 
Mouse No. 2 was given five series of ten tests each with a 
yellow card to indicate the right box and a red card at the 
entrance to the wrong box. At first he chose the red almost 
uniformly, and at no time during these fifty tests did he ex- 
hibit ability to choose the right box by color discrimination. 
I present the results of these series in Table 16, because they 
indicate a fact to which I shall have to refer repeatedly later, 
namely, that the brightness values of different portions of 
the spectrum are not the same for the dancer as for us. Pre- 
vious to this yellow-red training, No. 2, as a result of ten days 
of white-black training (two tests per day), had partially 
learned to go to the brighter of the two electric-boxes. It is 
possible therefore that the choice of the box in the case of 
these color experiments was in reality the choice of what 
appeared to the mouse to be the brighter box. If this were 
not true, how are the results of Table 16 to be accounted for? 

TABLE 16 

Yellow-Red Tests 

In Color Discrimination Box with 6 by 3 cm. Pieces of Hering 
Papers at Entrances to Boxes 

No. 2 



Series 


Date 


Right 
(Yellow) 


Wrong 
(Red) 


I 


Jan. 16 


I 


9 


2 


17 


3 


7 


3 


18 


4 


6 


4 


19 


5 


5 


5 


20 


5 


5 



These were the only Hering papers used in my experiments. 



140 The Dancing Mouse 

Without further mention of the many experiments which 
were necessary for the perfecting of this method of testing 
color vision, I may at once present the final results of the tests 
which were made with reflected light. These tests were 
made with the discrimination apparatus in essentially the 
same way as were the brightness discrimination tests of 
Chapter VII. 

In all of the color experiments, unless otherwise stated, 
a series of ten tests each day was given, until satisfactory 
evidence of discrimination or proof of the lack of the ability 
to discriminate had been obtained. The difficulties of getting 
conclusive evidence in either direction will be considered in 
connection with the results themselves. For all of these 
tests with reflected light the Milton Bradley colored papers 
were used. These colored papers were pasted on white 
cardboard carriers. I shall designate, in the Bradley nomen- 
clature, the papers used in each experiment. 

With colored cardboards inside the electric-boxes as well 
as at their entrances (see Figure 14 for position of cardboards) 
blue-orange tests were given to Nos. 2 and 3 until they dis- 
criminated perfectly. The papers were Bradley's blue tint 
No. I and orange. Number 2 was perfect in the twelfth 
series (Table 17), No 3 in the fourteenth and again in the 
sixteenth. They were then tested with a special brightness 
check series which was intended by the experimenter to 
reveal any dependence upon a possible brightness difference 
rather than upon the color difference of the boxes. 

The nature of this brightness check series, as well as the 
results which No. 2 gave when tested by it, may be appre- 
ciated readily by reference to Table 18. Tint No. i of the 
blue, which is considerably brighter, in my judgment, than 
the Bradley blue, was replaced at intervals in this series by 
the latter. For it was thought that in case the mouse were 



The Sense of Sight : Color Vision 141 



TABLE 17 
Light Blue-Orange Tests in Color Discrimination Box 





Date 
1906 


Nc 


. 2 


No. 3 


Series 


Right 
(Light 
Blue) 


Wrong 
(Orange) 


Right 
(Light 
Blue) 


Wrong 
(Orange) 


I 


Jan. 26 




3 


I 


9 


2 

3 


27 
28 


^ 


3 
3 


5 
6 


5 
4 


4 


29 




3 


7 


3 


5 


30 




3 


4 


6 


6 

7 
8 


31 

Feb. I 

2 


10 

9 
8 




I 
2 


7 
7 
6 


3 
3 
4 


9 


3 


9 


I 


9 


I 


10 
II 


5 
6 


7 
8 


3 
2 


5 
' 5 


5 
5 


12 
Special bi 


7 
rightness check s 


10 
eries (see 1 



'able 18) 


5 


5 


13 1 8 
Special light blue-dark blu 


10 
e series 


1 


7 


3 


14 


9 


8 


2 


10 





15 
Special li^ 


10 
jht blue-dark blu 


9 
e series 


I 


9 


I 


16 


II 


9 


I 


10 













Special brightness 
check series 


17 


12 


10 





9 1 I 



choosing the blue of the series because it seemed brighter 
than the orange, this substitution might mislead it into choos- 
ing the orange. These blues are referred to in the table 
as light blue (tint No. i) and dark blue (standard blue). 
Again a change in the opposite direction was made by sub- 
stituting Bradley red for orange. As this was for the human 



142 



The Dancing Mouse 



eye the substitution of a color whose brightness was consider- 
ably less than that of the orange, it seemed possible that the 
mouse, if it had formed the habit of choosing the box which 
seemed the darker, might by this change be misled into choos- 
ing the red instead of the light blue. In a word, changes 
in the conditions of the experiments were made in such a way 

TABLE i8 

Light Blue-Orange 

Brightness check series Mouse No. 2, Series 13 

Feb. 8, 1906 



Test 


Condition 


Right 


Wrong 


I 


Light blue on right 








Orange on left 


Right 


— 


2 


Light blue on left 








Orange on right 


Right 


— 


3 


Light blue on right 








Red substituted for orange 


Right 


— 


4 


Light blue on left 








Red substituted for orange 


Right 


— 


5 


Dark blue on right 








Orange on left 


Right 


— 


6 


Dark blue on right 








Orange on left 


Right 


— 


7 


Dark blue on left 








Orange on right 


Right 


— 


8 


Dark blue on right 








Red substituted for orange 


Right 


— 


9 


Dark blue on left 








Red substituted for orange 


Right 


— 


10 


Dark blue on left 








Red substituted for orange 


Right 


— 




Totals 


10 






The Sense of Sight: Color Vision 143 

that now one color, now the other, appeared to be the brighter. 
But I did not attempt to exclude brightness discrimination 
on the part of the mouse by dependence upon the human 
judgment of brightness equality, for it is manifestly unsafe 
to assume that two colors which are of the same brightness 
for the human eye have a like relation for the eye of the 
dancer or of any other animal. My tests of color vision have 
been conducted without other reference to human standards 
of judgment or comparisons than was necessary for the de- 
scription of the experimental conditions. In planning the 
experiments I assumed neither likeness nor difference be- 
tween the human retinal processes and those of the dancer. 
It was my purpose to discover the nature of the mouse's 
visual discriminative ability. 

As is indicated in the tables, neither the substitution of 
dark blue for light blue, nor the replacement of the orange 
by red or dark blue rendered correct choice impossible, al- 
though certain of the combinations did render choice ex- 
tremely difficult. In other words, despite all of the changes 
which were made in the brightness of the cardboards in 
connection with the light blue-orange tests, the mice con- 
tinued to make almost perfect records. What are we to 
conclude from this? Either that the ability to discriminate 
certain colors is possessed by the dancer, or that for some 
reason the tests are unsatisfactory. If it be granted that the 
possibility of brightness discrimination was excluded in the 
check series, the first of these alternatives apparently is forced 
upon us. That such a possibility was not excluded, later 
experiments make perfectly clear. The fact was that not 
even in the check series was the brightness value of the orange 
as great as that of the blue. Consequently the mice may I 
have chosen the brighter box each time while apparentlyj 
choosing the blue. 



144 The Dancing Mouse 

Although conclusive proof of the truth of this statement 
is furnished only by later experiments, the results of the light 
blue-orange series, as given in Table 17, strongly suggest such 
a possibility. Mouse No. 3 had not been experimented 
with previous to these color discrimination tests. Her 
preference for the orange, v^hich in the case of the first series 
was 9 to I, consequently demands an explanation. If she 
had been trained previously to choose the white instead of 
the black, as was true of No. 2, it might be inferred that she 
went to the orange box because it appeared brighter than the 
blue. As this explanation is not available, we are driven 
back upon the results of the white-black preference tests in 
Chapter VII, which proved that many dancers prefer the 
black to the white. This may mean that they prefer the 
lower degree of brightness or illumination, and if so it might 
be argued, in turn, that the orange was chosen by No. 3 be- 
cause it appeared darker than the blue. Since, as has al- 
ready been stated, the orange was far brighter for me than 
the blue, this would also mean that the brightness values 
of different colors are not the same for man and mouse. 

Practically the same kind of color tests as those described 
for Nos. 2 and 3 were given to Nos. 1000 and 5. The re- 
sults appear in Table 19. These tests followed upon the 
formation of a habit to choose white instead of black (that 
is, the greater brightness). From the first both No. 1000 
and No. 5 chose the light blue in preference to the orange 
or the red. It therefore seems probable that the former 
was considerably brighter than the latter. Number 1000, 
to be sure, was led into three erroneous choices by the bright- 
ness check series (series 7), but, on the other hand. No. 5 
was not at all disturbed in her choices by similar check tests. 
It seems natural to conclude from these facts that both of these 
mice chose the blue at first because of its relatively greater 



The Sense of Sight : Color Vision 



45 



p 

B brightness, and that they continued to do so for the same 
reason. In other words, their behavior indicates that the 
brightness check tests were valueless because not enough 
allowance had been made for the possible differences between 
: the vision of mouse and man. 



TABLE 19 
Light Blue-Orange and Dark Blue-Red Tests 





Date 


Condition 


No. 


1000 


No 


• s 


Series 


Right 


Wrong 


Right 


Wrong 








(Light 
Blue or 


(Orange 


(Light 
Blue or 


(Orange 








Dark 
Blue) 


Red) 


Dark 

Blue) 


Red) 


I 


Jan. 25 


Blue-red 


8 


2 


10 





2 


26 


Blue-red or 














Light blue-orange 


10 





10 





3 


27 


Light blue-orange 


10 





5 


5 


4 


29 


Light blue-orange 


9 


I 


8 


2 


5 


30 


Light blue-orange 


10 





8 


2 


6 


31 


Light blue -orange 


10 





10 





7 


Feb. I 


Light blue-orange or 














Dark blue-red 


. 7 


3 


10 






If only the final result , of my experiments with the dancer 
and the conclusions to which they lead were of interest, all 
of this description of experiments which served merely to 
clear the ground and thus make possible crucial tests might 
be omitted. It has seemed to me, however, that the history 
of the investigation is valuable, and I am therefore presenting 
the evolution of my methods step by step. To be sure, not 
every detail of this process can be mentioned, and only a 
few of the individual results can be stated, but my purpose 
will have been fulfilled if I succeed in showing how one 
method of experimentation pointed the way to another, and 



146 The Dancing Mouse 

how one set of results made possible the interpretation of 
others. 

As the results of my color vision experiments seemed to 
indicate that the red end of the spectrum appears much 
darker to the dancer than to us, tests were now arranged 
with colors from adjacent regions of the spectrum, green and 
blue. The papers used were the Bradley green and tint 
No. I of the blue. They were not noticeably different in 
brightness for the human eye. Green marked the box to 
be chosen. Three of the individuals which had previously 
been used in the light blue-orange series, and which therefore 
had perfect habits of going to the light blue, were used for 
the green-light blue tests. Of these individuals. No. 1000 
became inactive on the fifth day of the experiment, and the 
tests with him were discontinued. Twenty series were given 
to each of the other mice, with the results which appear in 
Table 20. To begin with, both No. 4 and No. 5 exhibited a 
preference for the light blue, as a result of the previous light 
blue-orange training. As this preference was gradually 
destroyed by the electric shock which was received each time 
the light blue box was entered, they seemed utterly at a loss 
to know which box to enter. Occasionally a record of six, 
seven, or even eight right choices would be made in a series, 
but in no case was this unquestionably due to color discrim- 
ination ; usually it could be explained in the light of the order 
of the changes in the positions of the cardboards. For ex- 
ample, series 9, in which No. 5 made a record of 8 right and 
2 wrong, had green on the right for the first three tests. The 
animal happened to choose correctly in the first test, and 
continued to do so three times in succession simply because 
there was no change in the position of the cardboards. I 
have occasionally observed a record of seven right choices re- 
sult when it was perfectly evident to the observer that the mouse 



The Sense of Sight: Color Vision 147 

could not discriminate visually. It was to avoid unsafe conclu- 
sions and unfair comparisons, as the result of such misleading 
series, that three perfect series in succession v^ere required 
as evidence of a perfectly formed habit of discrimination. 

TABLE 20 
Green-Light Blue Tests 







Date 
1906 


No. 


lOOO 


No. 4 


Nc 


• 5 


Series 


Right 


Wrong 


Right 


Wrong 


Right 


Wrong 






(Green) 


(Blue) 


(Green) 


(Blue) 


(Green) 


(Blue) 


I 


Feb. 3 


2 


8 


3 


7 


3 


7 


2 


5 


7 


3 


5 


5 


5 


5 


3 


6 


5 


5 


6 


4 


5 


5 


4 


7 


5 


5 


5 


5 


5 


5 


5 


8 


2 


8 


5 


5 


4 


6 


6 


9 






7 


3 


7 


3 


7 


10 






4 


6 


3 


7 


8 


10 






6 


4 


4 


6 


9 


12 






6 


4 


8 


2 


10 


13 






6 


4 


6 


4 


II 


14 






5 


5 


3 


7 


12 


15 






6 


4 


7 


3 


13 


16 






5 


5 


7 


3 


14 


17 






3 


7 


6 


4 


15 


19 






6 


4 


6 


4 


16 


20 






7 


3 


5 


5 


17 


21 






4 


6 


8 


2 


18 


22 






3 


7 


4 


6 


19 


23 






6 


4 


4 


6 


20 


24 






6 


4 


5 


5 





Twenty series, 200 tests for each of the individuals in the 
experiment, yielded no evidence whatever of the dancer's 
ability to tell green from blue. As it has already been proved 
that they readily learn to choose the right box under dis- 
criminable conditions, it seems reasonable to conclude either 



148 



The Dancmg Mouse 



that they lack green-blue vision, or that they have it in a 
relatively undeveloped state. 

If it be objected that the number of training tests given Was 
too small, and that the dancer probably v^ould exhibit dis- 
crimination if it were given 1000 instead of 200 tests in such 
an experiment, I must reply that the behavior of the animal 
in the tests is even more satisfactory evidence of its inability 
to choose than are the results of Table 20. Had there been 
the least indication of improvement as the result of 200 tests, 
I should have continued the experiment ; as a matter of fact, 
the mice each day hesitated more and more before choosing, 
and fought against being driven toward the entrance to the ex- 
periment box. That they were helpless was so evident that it 
would have been manifestly cruel to continue the experiment. 

TABLE 21 

Violet-Red Tests 
With Odor of All Cardboards the Same 





Date 


No 


• 7 


No. 


998 


Series 


Right 


Wrong 


Right 


Wrong 






(Violet) 


(Red) 


(Violet) 


(Red) 


A 


Mar. 7 


8 


2 


5 


5 


B 


7 


3 


7 


2 


8 


I 


14 


3 


7 


6 


4 


2 


15 


4 


6 


4 


6 


3 


16 


5 


5 


5 


5 


4 


19 


4 


6 


4 


6 


5 


20 


5 


5 


6 


4 


6 


21 


4 


6 


8 


2 


7 


22 


8 


2 


4 


6 


8 


23 


4 


6 


6 


4 


9 


24 


6 


4 


4 


6 


10 


25 


4 


6 


6 


4 



The Sense of Sight : Color Vision 149 

Further color tests with reflected light were made with 
violet and red. Two dancers, Nos. 998 and 7, neither of 
which had been in any experiment previously, were subjected 
to the ten series of tests whose results are to be found in Table 
21. In this experiment the cardboards used had been coated 
with shellac to obviate discrimination by means of odor. 
It is therefore impossible to give a precise description of the 
color or brightness by referring to the Bradley papers.^ 
Both the violet and the red were rendered darker, and ap- 
parently less saturated, by the coating. 

These violet-red tests were preceded by two series of prefer- 
ence tests {A and 5), in which no shock was given and escape 
was possible through either electric-box. Although the re- 
sults of these preference tests as they appear in Table 21 seem 
to indicate a preference for the red on the part of No. 998, 
examination of the record sheets reveals the fact that neither 
animal exhibited color preference, but that instead both 
chose by position. Number 998 chose the box on the right 
15 times in 20, and No. 7 chose the box on the left 15 times 
in 20.' 

Ten series of tests with the violet-red cardboards failed to 
furnish the least indication of discrimination. The experi- 
ment was discontinued because the mice had ceased to try 
to discriminate and dashed into one or the other of the boxes 
on the chance of guessing correctly. When wrong they 
whirled about, rushed out of the red box and into the violet 
immediately. They had learned perfectly as much as they 
were able to learn of what the experiment required of them. 
Although we are not justified in concluding from this experi- 
ment that dancers cannot be taught to distinguish violet 
from red, there certainly is good ground for the statement 

^ The violet was darker than Bradley's shade No. 2, and the red was 
lighter than Bradley's red. 



150 The Dancing Mouse 

that they do not readily discriminate between these 
colors. 

The experiments on color vision which have been described 
and the records which have been presented will suffice to 
give the reader an accurate knowledge of the nature of the 
results, only a few of which could be printed, and of the meth- 
ods by which they were obtained. 

In brief, these results show that the dancer, under the con- 
ditions of the experiments, is not able to tell green from blue, 
or violet from red. The evidence of discrimination furnished 
by the light blue-orange tests is not satisfactory because the 
conditions of the experiment did not permit the use of a suffi- 
ciently wide range of brightnesses. It is obvious, therefore, 
that a method of experimentation should be devised in which 
the experimenter can more fully control the brightness of the 
colors which he is using. I shall now describe a method 
in which this was possible. 



CHAPTER X 
The Sense of Sight: Color Vision (Continued) 

There are three well-known ways in which colors may 
be used as stimuli in experiments on animals: by the use 
of colored papers (reflected light) ; by the use of a prism 
(the spectrum which is obtained may be used as directly 
transmitted or as reflected light) ; and by the use of light 
filters (transmitted light). In the experiments on the color 
vision of the dancer which have thus far been described only 
the first of these three methods has been employed. Its 
advantages are that it enables the experimenter to work in 
a sunlit room, with relatively simple, cheap, and easily 
manipulated apparatus. Its, chief disadvantages are that 
the brightness of the light can_ neither b£_ re gulated nor 
measured with ease and accuracy. The use of the second 
method, which in many respects is the most desirable of the 
three, is impracticable for experiments which require as large 
an illuminated region as do those with the mouse; I was 
therefore limited to the employment of light filters in my 
further tests of color discrimination. 

The form of filter which is most conveniently handled is 
the colored glass, but unfortunately few glasses which are 
monochromatic are manufactured. Almost all of our so- 
called colored glasses transmit the light of two or more regions 
of the spectrum. After making spectroscopic examinations 
of all the colored glasses which were available, I decided 
that only the ruby glass could be satisfactorily used in my 

151 



152 The Da7ichig Mouse 

experiments. With this it was possible to get a pure red. 
Each of the other colors was obtained by means of a filter, 
which consisted of a glass box filled with a chemical solution 
which transmitted light of a certain wave length. 

For the tests with transmitted light the apparatus of 
Figures 20 and 21 was constructed. It consisted of a re- 
action-box essentially the same as that used in the brightness 
vision tests, except that holes were cut in the ends of the 
electric-boxes, at the positions G and R of Figure 20, to per- 
mit the hght to enter the boxes. Beyond the reaction-box 
was a long light-box which was divided lengthwise into two 
compartments by a partition in the middle. A slit in the 
cover of each of these compartments carried an incandescent 
lamp L (Figure 20). Between the two lamps, Z, Z, and 
directly over the partition in the light-box was fastened a 
millimeter scale, 5, by means of which the experimenter 
could determine the position of the lights with reference to 
the reaction-box. The light-box was separated from the 
reaction-box by a space 6 cm. wide in which moved a narrow 
wooden carrier for the filter boxes. This carrier, as shown in 
Figure 20, could be moved readily from side to side through 
a distance of 20 cm. The filter boxes, which are represented 
in place in Figures 20 and 21, consisted of three parallel- 
sided glass boxes 15 cm. long, 5 cm. wide, and 15 cm. deep. 
Each box contained a substance which acted as a ray filter. 
Tightly fitted glass covers prevented the entrance of dust and 
the evaporation of the solutions in the boxes. Figures 20 
and 21 represent the two end boxes, 7?, i?, as red light filters 
and the middle one, G, as a green light filter. Three filters 
were used thus side by side in order that the position of a 
given color with reference to the electric-boxes might be 
changed readily. As the apparatus was arranged, all the 
experimenter had to do when he wished to change from 




Figure 20. — Color discrimination apparatus. A, nest-box; B, entrance 
chamber; i?, i?, red filters; G, green filter; L, L, incandescent lamps in light- 
box; 5, millimeter scale on light-box; /, door between A and B\ O, O, doors 
between alleys and A. 

153 



154 



The Danchig Mouse 




Figure 21. — Ground plan of color 
discrimination apparatus. £, £, exits 
from electric-boxes. LB, light-box; 
R, G, R, filter boxes on carrier; L, left 
electric-box; R, right electric-box; IC, 
induction apparatus; C, electric cell; 
K, key ; S, millimeter scale. 



green-left, red-right to green- 
right, red-left was to push the 
carrier towards the right until 
the green filter covered the 
hole on the right at the end of 
the electric-box. When this 
had been accomplished the red 
filter at the left end of the 
carrier covered the hole on the 
left at the end of the electric- 
box. Thus quickly, noiselessly, 
easily, and without introducing 
any other change in conditions 
than that of the interchange of 
lights, the experimenter was 
able to shift the positions of 
his colored lights at will. 

In the tests which are now 
to be reported, three portions 
of the spectrum were used : 
the red end, the blue-violet 
end, and a middle region, 
chiefly green. The red light 
was obtained by the use of a 
filter which was made by plac- 
ing two plates of ruby glass in 
one of the glass boxes, filling the 
box with filtered water and then 
sealing it to prevent evapora- 
tion. The blue-violet was ob- 
tained by the use of a filter box 
which contained a 5 per cent 
solution of copper ammonium 



The Sense of Sight: Color Vision 155 

sulphate. The green, which, however, was not monochro- 
matic, was obtained by the use of a filter box which con-. 
tained a saturated solution of nickel nitrate. These three 
sets of filters were examined spectroscopically both before 
the experiments had been made and after their completion.^ 
ThQ red filters, of which I had two for shifting the lights, 
transmitted only red light. The blue-violet filters, two also, 
at first appeared to transmit only portions of the blue and 
violet of the spectrum, but my later examination revealed a 
trace of green. It is important to note, however, that the 
red and the blue-violet filters were mutually exclusive in the 
portions of the spectrum which they transmitted. Of all 
the filters used the green finally proved the least satisfactory. 
I detected some yellow and blue in addition to green in my 
first examination, and later I discovered a trace of red. Ap- 
parently the transmitting power of the solutions changed 
slightly during the course of the experiments. On this 
account certain solutions are undesirable for experiments 
on color vision, for one must be certain of the constancy of 
the condition of stimulation. It is to be understood, of 
course, that each of the three filters transmitted, so far as 
the eye is concerned, only the color named. I consider the 
red filter perfectly satisfactory, the blue- violet very good, and 
the green poor Henceforth, in testing color vision in ani- 
mals, I shall make use of colored glasses as filters, if it is in 
any way possible to obtain or have manufactured blue, green, 
and yellow glasses which are as satisfactory as the ruby. 

The apparatus needs no further description, as its other 
important features were identical with those of the reflected 
light experiment box. The use of artificial light for the 
illumination of the electric-boxes made it necessary to con- 
duct all of the following tests in a dark-room. The method 

* A Janssen-Hoffman spectroscope was used. 



156 . The Dancmg Mouse 

of experimentation was practically the same as that already 
described. A mouse which had been placed in A by the 
experimenter was permitted to enter B and thence to return 
to A by entering one of the electric-boxes, the red or blue or 
green one, as the case might be. Mistakes in choice were 
punished by an electric shock. One further point in the 
method demands description and discussion before the re- 
sults of the tests are considered, namely, the manner of 
regulating and measuring the brightness of the lights. 

Regulating brightness with this apparatus was easy enough ; 
measuring it accurately was extremely difficult. The experi- 
menter was able to control the brightness of each of the two 
colored lights which he was using by changing the position 
or the power of the incandescent lamps in the light-box. 
The position of a lamp could be changed easily between tests 
simply by moving it along toward or away from the electric- 
box in the sht which served as a lamp carrier. As the dis- 
tance from the entrances of the electric-boxes to the further 
'end of the light-box was 120 cm., a considerable range or 
variation in brightness was possible without change of lamps. 
Ordinarily it was not necessary to change the power of the 
lamps, by replacing one of a given candle power by a higher 
or lower, during a series of tests. Both the candle power of 
the lamps and their distance from the filters were recorded 
in the case of each test, but for the convenience of the reader 
I have reduced these measurements to candle meters * and 
report them thus in the descriptions of the experiments. 

But measuring the actual brightness of the red light or 
the green light which was used for a particular series of tests, 
and the variations in their brightnesses, was not so simple 
a matter as might appear from the statements which have 
just been made. The influence of the light filters themselves 

* The illuminating power of a standard candle at a distance of one meter. 



The Sense of Sight : Color Visioft 157 

upon the brightness must be taken into account. The two 
red filters were aHke in their influence upon the hght which 
entered them, for they were precisely alike in construction, 
and the same was true of the two blue-violet filters. The 
same kind of ruby glass was placed in each of the former, 
and a portion of the same solution of copper ammonium 
sulphate was put into each of the filter boxes for the latter. 
But it is difficult to say what relation the diminution in 
brightness caused by a red filter bore to that caused by a 
blue-violet or a green filter. My only means of comparison 
was my eye, and as subjective measurement was unsatis- 
factory for the purposes of the experiment, no attempt was 
made to equalize the amounts of brightness reduction caused 
by the several filters. So far as the value of the tests them- 
selves, as indications of the condition of color vision in the 
dancer is concerned, I have no apology for this lack of measure- 
ment, but I do regret my inability to give that accurate ob- 
jective statement of brightness values which would enable an- 
other experimenter with ease and certainty to repeat my tests. 
The nearest approach that it is possible for me to make to 
such an objective measurement is a statement of the com- 
position and thickness of the filters and of the candle-meter 
value of the light when it entered the filter. The distance 
from this point to the entrance to the electric-box was 20 cm. 
To sum up and state clearly the method of defining the 
brightness of the light in the following experiments: the 
candle-meter value of each light by which an electric-box 
was illuminated, as determined by the use of a Lummer- 
Brodhun photometer and measurements of the distance of 
the source of light from the filter, is given in connection with 
each of the experiments. This brightness value less the 
diminution caused by the passage of the light through a 
filter, which has been defined as to composition and thick- 



158 



The Dancing Mouse 



ness of the layer of solution, gives that degree of brightness 
by which the electric-box was illuminated. 

Tests of the dancer's ability to discriminate green and 
blue ^ in the transmitted light apparatus were made with four 
animals. An incandescent lamp marked i6-candle-power 
was set in each of the light-boxes. These lamps w^e then 
so placed that the green and the blue seemed to be of equal 
brightness to three persons who were asked to compare them 
carefully. Their candle-meter values in the positions selected 
were respectively i8 and 64, as appears from the statement of 
conditions at the top of Table 22. 

TABLE 22 

Green -Blue Tests 

Brightnesses Equal for Human Eye 

Green 18 candle meters Blue 64 candle meters 





Date 
1Q06 


No 


10 


No 


II 


Series 


Right 


Wrong 


Right 


Wrong 






(Green) 


(Blue) 


(Green) 


(Blue) 


AandB^ 


April 2 


10 


10 


12 


8 


I 


3 


6 


4 


5 


5 


2 


4 


5 


5 


6 


4 


3 


5 


5 


5 


5 


5 


4 


6 


5 


5 


5 


5 


5 


7 


7 


3 


5 


. 5 


6 


8 


7 


3 


3 


7 


7 


9 


7 


3 


5 


5 


8 


10 


3 


7 


7 


3 


9 


II 


5 


5 


4 


6 


10 


12 


5 


5 


6 


4 



^ Hereafter the light transmitted by the blue-violet filter will be referred 
to for convenience as blue. 

^ A single preference series of twenty tests. 



The Sense of Sight : Color Vision 159 

Numbers 10 and 11 exhibited no preference for either of 
these colors in the series of 20 tests which preceded the 
training tests, and neither of them gave evidence of abihty 
to discriminate as the result of ten series of training tests. 
In this case, again, the behavior of the animals was as strongly 
against the inference that they can tell green from blue as 
are the records of choices which appear in the table. Granted, 
that they are unable to discriminate green from blue when 
these colors are of about the same brightness for the human 
eye, what results when they differ markedly in brightness? 
Table 23 furnishes a definite answer to this question. Num- 
bers 5 and 12 were given eight series of green-blue tests 
with each light at 18 candle meters. Little, if any, evidence 
of discrimination appeared. Then, on the supposition that 
the difference was not great enough for easy discrimination, 
the blue light was reduced almost to o, the green being left 
at 18. The tests (series 9) immediately indicated discrimi- 
nation. For series 10 the green was made 64 candle meters, 
the blue 18, and again there was discrimination. These re- 
sults were so conclusively indicative of the lack of color 
vision and the presence of brightness vision, that there ap- 
peared to be no need of continuing the experiment further. 

Accepting provisionally the conclusion that the dancers 
cannot tell green from blue except by brightness differences, 
we may proceed to inquire whether they can discriminate 
other colors. Are green and red distinguishable? 

Green-red discrimination now was tested by a method 
which it was hoped might from the first prevent dependence 
upon brightness. The light in the light-box on the left was 
so placed that it had a value of 18 candle meters, that in the 
light-box on the right so that it had a value of 1800 candle 
meters. Neither light was moved during the first four series 
of the green-red tests which were given to Nos. 151 and 152. 



i6o 



The Dancing Mouse 



TABLE 23 

Green-Blue Tests 

Brightnesses Different for Human Eye 

Green 18 candle meters Blue 18 candle meters 





Date 
1906 


No 


• 5 


No 


12 


Series 


Right 


Wrong 


Right 


Wrong 






(Green) 


(Blue) 


(Green) 


(Blue) 


I 


April 10 


6 


4 


5 


5 


2 


II 


5 


5 


7 


3 


3 


12 


6 


4 


7 


3 


4 


13 


4 


6 


7 


3 


5 


14 


7 


3 


5 


5 


6 


15 


4 


6 


6 


4 


7 


16 


6 


4 


8 


2 


8 


17 


. 5 


5 


4 


6 



As it was now evident that the intensity difference was not sufficient 
to render discrimination easy, the blue was reduced to o, and the green 
left at 18. 

9|i7 |7!3I8|2 

Now the brightnesses were made, green 64, blue 18, just the reverse 
of those of series of Table 22. 



10 



17 



8 



8 



Each of these series consisted of 20 tests instead of 10. As 
a result of the arrangement of the Hghts just mentioned, the 
green appeared to me very much brighter than the red when 
it was on the right and very much darker when it was on 
the left. If this were true for the mouse also, it is difficult 
to see how it could successfully depend upon brightness for 
guidance in its choices. Such dependence would cause it to 
choose now the green, now the red. 

The first four series of green-red tests so clearly demon- 
strated discrimination, of some sort, that it was at once 



The Sense of Sight : Color Vision 1 6 1 

necessary to alter the conditions of the experiment. The 
only criticism of the above method of excluding brightness 
discrimination, of which I could think, was that the red at no 
time had been brighter than the green. In other words, that 
despite a value of 1800 candle meters for the red and only 
18 candle meters for the green, the latter still appeared the 
brighter to the mouse. To meet this objection, I made the 
extreme brightness values i and 1800 candle meters in some 
of the later series, of which the results appear in Table 24. 
From day to day different degrees of brightness were used, 
as is indicated in the second column of the table. Instead 
of having first one color and then the other the brighter, 
after the fourth series I changed the position of the lights 
each time the position of the filters was changed ; hence, the 
table states a certain brightness value for each color instead 
of for each electric-box. 

Series 5 to 14 so clearly indicated discrimination, that it 
seemed necessary to devise some other means than that of 
changing the brightnesses of the colored Hghts themselves 
to test the assumption that the animals were choosing the 
brighter light. I therefore removed the light filters so that the 
colors which had been present as conditions of discrimination 
were lacking, and arranged the apparatus so that first one box, 
then the other, was illuminated the more brightly. The pur- 
pose of this was to discover whether as the result of their 
green-red training the mice had acquired the habit of choos- 
ing uniformly either the lighter or the darker box. One 
series was given under the conditions of illumination specified 
in Table 24 with the result that the brighter box was chosen 
eight times in ten by No. 151 and every time by No. 152. 
Since neither of these individuals had previously been trained 
by white-black tests to go to the white, and since, furthermore, 
the dancers usually manifest a slight preference for the lower 



1 62 The Dancing Mouse 

instead of the higher illumination, this result may be inter- 
preted as indicative of dependence upon brightness in the 
previous color tests. It looks very much indeed as if the 
green had been chosen, not because of its greenness, but on 
account of its relatively greater brightness. 

This test of brightness preference was follov^ed by two 
series, i6 and 17, under conditions similar to those of the 
first four series of the table. For series 16 the value of the 
light in the left box was i candle meter, that of the light in 
the right box 1800 candle meters. Discrimination was per- 
fect. For series 17 the value for the left remained at i candle 
meter, but that of the right box was decreased to o. In this 
series No. 152 was entirely at a loss to know which box to 
choose. Of course this was an entirely new set of conditions 
for choice, namely, a colored box, the green or the red as the 
case might be, beside a dark box, the one which was not 
illuminated. If the mice really had been choosing coi^rectly 
because of a habit of avoiding the red or of seeking the green, 
this method should bring out the fact, for the red box, since 
with it the disagreeable electric shock had always been asso- 
ciated, should be a box to be avoided. For No. 151 this 
seemed to be the case. 

Series 23 to 27 of Table 24 were given as final and crucial 
tests of the relation of brightness discrimination to color dis- 
crimination. As it is not possible to express in a simple 
formula the conditions of the tests, a sample series which 
indicates the brightness of the colors in each of the twenty 
tests of a series, and in addition the results given by No. 151 
in the first of these final series, is reproduced in Table 25. 
For an animal which had presumably learned perfectly to 
choose green in preference to red, the record of 8 mistakes 
in 20 choices as a result of changes in relative brightness is 
rather bad, and it renders doubtful the existence of color 
discrimination in any of these experiments. No. 152 showed 



The Sense of Sight: Color Vision 163 



TABLE 24 

Green-Red Tests 

Brightnesses Extremely Different for Human Eye 

Intensities are given in candle meters (cm.) 





Date 


Conditions 


No. 


151 


No. 


152 


Series 


Right 


Wrong 


Right 


Wrong 




, 




(Green) 


(Red) 


(Green) 


(Red) 


I 


April 26 


18 cm. on left 














1800 cm. on right 


II 


9 


7 


13 


2 


27 


Same 


16 


4 


16 


4 


3 


28 


Same 


20 





17 


3 


4 


29 


Same 


19 


I 


19 


I 


5 


30 


Green 18 cm. 














Red 18 cm. 


9 


I 


10 





6 


30 


Green 64 cm. 














Red 18 cm. 


9 


I 


8 


2 


7 


May I 


Green 6 cm. 














Red 1500 cm. 


7 


3 


9 


I 


8 


I 


Green 4 cm. 














Red 1500 cm. 


8 


2 


7 


3 


9 


2 


Both varied from 














4 to 1500 cm. 


18 


2 


18 


2 


10 


3 


Green 2 cm. 














Red 1800 cm. 


6 


4 


7 


3 


II 


3 


Same 


10 





10 





12 


4 


Same 


7 


3 


8 


2 


13 


4 


Same 


8 


2 


6 


4 


14 


5 


Green i cm. 














Red 1800 cm. 


19 


I 


19 


I 



Filters were now removed. An illumination of 15 cm. was estab- 
lished on one side and an illumination of o on the other side, in order to 
ascertain whether the mice would choose the brighter box. This was 
done to test the assumption that the green in the previous tests had 
always appeared brighter to the mice than did the red, and that in 
consequence they had chosen the brighter box instead of the green box. 



164 



The Dancing Mouse 



TABLE 24 — Continued 





Date 


Conditions 


No. 


151 


No. 


^52 


Series 


Right 


Wrong 


Right 


Wronc. 








(Green) 


(Red) 


(Green) 


(Red) 


15 


May 5 


Brighter 15 cm. 
Darker cm. 


8' 


2" 


10^ 


G^ 


16 


5 


I cm. on left 














1800 cm. on right 


10 





10 





17 


5 


I cm. on left 














cm. on right 


9 


I 


4 


6 


18 


8 


Green 18 cm. 














Red 18 cm. 


19 


I 


17 


3 


19 


9 


Same 


9 


I 


9 


I 


20 


9 


Same 


10 





10 





21 


10 


Same 


ID 





10 





22 


II 


Same 


10 





10 





23 


June I 


Both varied from 














I to 1800 cm. 


12 


8 


10 


10 


24 


2 


Same 


18 


2 


14 


6 


25 


3 


Both varied from 














2 to 1800 cm. 


19 


I 


17 


3 


26 


4 


Same 


17 


3 


17 


3 


27 


5 


Same 


18 


2 


18 


2 



no ability whatever to choose the green in the first of the 
series (series 23 of Table 24) of which that of Table 25 is a 
sample. His record, 10 mistakes in 20 choices, was even 
poorer than that of No. 151. That both of these mice 
learned to choose fairly accurately in these final tests is 
shown by the results of series 24, 25, 26, and 27. I must 
admit, however, that these records indicate little abihty on 
the part of the animals to discriminate colors. 

These long-continued and varied tests with Nos. 151 and 

^ Brighter. ^ Darker. 



The Sense of Sight : Color Vision 165 



152 revealed three facts: that the mice depend chiefly upon 
brightness differences in visual discrimination; that they 
probably have something which corresponds to our red-green 
vision, although their color experience may be totally unlike 
ours ; and that the red end of the spectrum seems much darker 
to them than to us, or, in other words, that the least refrangi- 
ble rays are of lower stimulating value for them than for us. 
So many of the results of my color experiments have 



TABLE 25 
Green-Red Tests 





June I, 1906 






No. I 


51 


Test 




Brightness Values in Candle 


Right 


Wrong 






Meters 


(Green) 


(Red) 


I 


Green on left 


Green 4, 


Red 448 


Right 


— 


2 


Green on right 


Green 448, 


Red 4 


Right 


— 


3 


Green on right 


Green 4, 


Red 448 


Right 


— 


4 


Green on left 


Green 448, 


Red 4 


Right 


— 


5 


Green on left 


Green 3, 


Red 1800 


— 


Wrong 


6 


Green on right 


Green 1800, 


Red 3 


— 


Wrong 


7 


Green on right 


Green 3, 


Red 1800 


— 


Wrong 


8 


Green on left 


Green 1800, 


Red 3 


Right 


— 


9 


Green on right 


Green 5, 


Red 34 


Right 


— 


10 


Green on left 


Green 34, 


Red 5 


Right 


— 


II 


Green on right 


Green 6, 


Red 74 


Right 


— 


12 


Green on left 


Green 74, 


Red 6 


Right 


— 


13 


Green on left 


Green 4, 


Red 448 


— 


Wrong 


14 


Green on right 


Green 448, 


Red 4 


Right 


— 


15 


Green on right 


Green 4, 


Red 448 


— 


Wrong 


16 


Green on left 


Green 448, 


Red 4 


Right 


— 


17 


Green on right 


Green 3, 


Red 1800 


— 


Wrong 


18 


Green on left 


Green 1800, 


Red 3 


— 


Wrong 


19 


Green on right 


Green 1800, 


Red 3 


— 


Wrong 


20 


Green on left 


Green 3, 


Red 1800 


Right 


— 




Totals 




12 


8 



1 66 The Dancing Mouse 

indicated the all-important role of brightness vision that I 
have hesitated to interpret any of them as indicative of true 
color discrimination. But after I had made all the varia- 
tions in brightness by which it seemed reasonable to suppose 
that the mouse would be influenced under ordinary condi- 
tions, and after I had introduced all the check tests which 
seemed worth while, there still remained so large a proportion 
of correct choices that I was forced to admit the influence of 
the quality as well as of the intensity of the visual stimulus. 

The first of the facts mentioned above, that brightness 
discrimination is more important in the life of the mouse 
than color discrimination, is attested by almost all of the 
experiments whose results have been reported. The second 
fact, namely, that the dancer p ossesse s something which for 
the present we may call red -green vision ^ also has been 
proved in a fairly satisfactory manner by both the reflected 
and the transmitted light experiments. I wish now to pre- 
sent, in Table 26, results which strikingly prove the truth of the 
statement that red appears darker to the dancer than to us. 

The brightness conditions which appeared to make the 
discrimination between green and red most difficult were, so 
far as my experiments permit the measurement thereof, green 
from I to 4 candle meters with red from 1200 to 1600. 
Under these conditions the red appeared extremely bright, 
the green very dark, to the human subject. 

According to the description of conditions in Table 26, 
Nos. 2 and 5 were required to distinguish green from red 
with the former about 3 candle meters in brightness and the 
latter about 1800 candle meters. In the eighth series of 20 
tests, each of these animals made a perfect record. As it 
seemed possible that they had learned to go to the darker 
of the two boxes instead of to the green box, I arranged the 
following check test. The filters were removed, the illumi- 



The Sense of Sight : Color Vision 167 

nation of one electric-box was made 74 candle meters, that 
of the other 3, and the changes of the lighter box from left 
to right were made at irregular intervals. In February, No. 2 
had been trained to go to the black in black-white tests, and 
at the same time No. 5 had been trained to go to the white 
in white-black tests. The results of these brightness check 
tests, as they appear in the table, series 8 a, are indeed 
striking. Number 2 chose the darker box each time; 
No. 5 chose it eight times out of ten. Were it not for the 
fact that memory tests four weeks after his black- white train- 
ing had proved that No. 2 had entirely lost the influence of 
his previous experience (he chose white nine times out of 
ten in the memory series), it might reasonably be urged that 
this individual chose the darker box because of his experi- 
ence in the black-white experiment. And what can be said 



TABLE 26 

Green-Red Tests 

Brightnesses Dififerent for Human Eye 





Date 


Brightness Values 


No 


. 2 


No 


• S 


Series 


Right 


Wrong 


Right 


Wrong 








(Green) 


(Red) 


(Green) 


(Red) 


I 


May 7 


Green 3 cm. 














Red 1800 cm. 


10 


10 


12 


8 


2 


8 


Same 


12 


8 


II 


9 


3 


9 


Same 


15 


5 


14 


6 


4 


10 


Same 


18 


2 


12 


8 


5 


II 


Same 


18 


2 


14 


6 


6 


12 


Same 


19 


I 


16 


4 


7 


13 


Same 


19 


I 


18 


2 


8 


14 


Same 


20 





20 






Brightness tests without colors were now given to determine whether 
the mice had been choosing the brighter or the darker instead of the green. 



1 68 



The Dancing Mouse 
TABLE 26 — Continued 





Date 


Brightness Values 


Nc 


). 2 


No. s 


Series 
















Right 


Wrong 


Right 


Wrong 








(Green) 


(Red) 


(Green) 


(Red) 


8a 


14 


Brighter 74 cm. 
Darker 3 cm. 


0* 


lO^ 


2" 


82 


9 


15 


3 cm. on left 














1800 cm. on right 


8 


12 


16 


4 


10 


16 


4 cm. on left 














36 cm. on right 


5 


5 


7 


3 


II 


16 


Green 4 cm. 














Red 36 cm. 


9 


I 


8 


2 


12 


17 


II cm. on left 














1800 cm, on right 


7 


3 


6 


4 


13 


17 


Green 11 cm. 














Red 1800 cm. 


9 


I 


8 


2 


14 


18 


Mixed values 














3 to 1800 cm. 


7 


3 


8 


2 


15 


19 


Same 


7 


3 


7 


3 


16 


20 


Same 


7 


3 


7 


3 


17 


21 


Same 


7 


3 


9 


I 


18 


22 


Same 


9 


I 


8 


2 


19 


23 


Same 


7 


3 


9 


I 


20 


24 


Same 


10 





8 


2 


21 


25 


Same 


10 





9 


I 


22 


26 


Same 


9 


I 


10 






in explanation of the choices of No. 5 ? I can think of no 
more reasonable way of accounting for this most unexpected 
result of the brightness tests than the assumption that both 
of these animals had learned to discriminate by brightness 
difference instead of by color. 

Immediately after the brightness series, the influence of 
making first one color, then the other, the brighter was studied. 

* Brighter. 2 Darker. 



The Sense of Sight: Color Vision 169 

Throughout series 9 the brightness value of the left box re- 
mained 3 candle meters, that of the right side 1800 candle 
meters. Number 2 was so badly confused by this change 
that his mistakes in this series numbered 12 ; No. 5 made 
only 4 incorrect choices. Then series after series was given 
under widely differing conditions of illumination. The ex- 
pression "mixed values," which occurs in Table 26 in 
connection with series 14 to 22 inclusive, means that the 
brightnesses of the green and the red boxes were changed 
from test to test in much the way indicated by the sample 
series of Table 25. In view of the results of these 22 series, 
320 tests for each of two mice, it is evident that the dancer 
is able to discriminate visually by some other factor than 
brightness. What this factor is I am not prepared to say. 
It may be something akin to our color experience, it may be 
distance effect. No other possibilities occur to me. 

Table 26 shows that discrimination was relatively easy for 
Nos. 2 and 5 with green at 3 candle meters and red at 1800. 
That their discrimination was made on the basis of the greater 
brightness of the red, instead of on the basis of color, is in- 
dicated by the results of the brightness check series 8a. 
Increase in the brightness of the green rendered discrimina- 
tion difficult for a time, but it soon improved, and by no 
changes in the relative brightness of the two colors was it 
possible to prevent correct choice. 

In addition to giving point to the statement that red ap- 
pears darker to the dancer than to us, the above experiment 
shows that the animals depend upon brightness when they 
can, and that their ability to discriminate color differences is 
extremely poor, so poor indeed that it is doubtful whether 
their records are better than those of a totally color blind 
person would be under similar conditions. Surely in view of 
such results it is unsafe to claim that the dancer possesses 
color vision similar to ours. 



170 



The Dancing Mouse 



Perfectly trained as they were, by their prolonged green- 
red tests, to choose the green, or what in mouse experience 
corresponds to our green, Nos. 2 and 5 offered an excellent 
opportunity for further tests of blue-green discrimination. 
For in view of their previous training there should be no 
question of preference for the blue or of a tendency to depend 
upon brightness in the series whose results constitute Table 27. 

To begin with, the blue and the green were made quite 

TABLE 27 
Blue-Green Tests 





Date 


Brightness Values 


No 


. 2 


No 


• 5 


Series 


Right 


Wrong 


Right 


Wrong 








(Blue) 


(Green) 


(Blue) 


(Green) 


I 


June I 


Blue 74 cm. 














Green 36 cm. 


3 


7 


3 


7 


2 


2 


Same 


5 


5 


4 


6 


3 


3 


Same 


5 


5 


6 


4 


4 


4 


Same 


6 


4 


3 


7 


5 


5 


Same 


6 


4 


5 


5 


6 


6 


Blue 21 cm. 














Green 21 cm. 


6 


4 


7 


3 


7 


7 


Same 


2 


8 


3 


7 


8 


8 


Same 


5 


5 


4 


6 


9 


9 


Same 


3 


7 


6 


4 


10 


10 


Same 


2 


8 


4 


6 


II 


12 


Same 


6 


4 


3 


7 


12 


13 


Blue 36 cm. 














Green 21 cm. 


3 


7 


4 


6 


13 


14 


Same 


5 


5 






14 


15 


Blue 62 cm. 
Green 21 cm. 


4 


6 






15 


16 


Same 


5 


5 






16 


17 


Same 


5 


5 






17 


18 


Same 


6 


4 







The Sense of Sight : Color Vision 171 

TABLE 27 — Continued 

Now, as a final test, blue and green glasses were placed over the 
electric-boxes, the brightness of the two was equalized for the human 
eye, and the tests of series 18 and 19 were given to No. 2: — 





Date 


Brightness Values 


Nc 


►. 2 


Series 


Right 


Wrong 








(Blue) 


(Green) 


18 


18 


Blue 62 cm. 










Green 21 cm. 


4 


6 


19 


19 


Same 


6 


4 


20 


20 


Blue 21 cm. 










Green 88 cm. 


2 


8 



The green was now made much the brighter. 



21 


21 


Blue 21 cm. 










Green i8oo cm. 


7 


3 


22 


23 


Same 


8 


2 



bright for the human subject, blue 74 candle meters, green 36. 
Later the brightness of both was first decreased, then increased, 
in order to ascertain whether discrimination was condi- 
tioned by the absolute strength of illumination. No evidence 
of discrimination was obtained with any of the several condi- 
tions of illumination in seventeen series of ten tests each. 

On the supposition that the animals were blinded by the 
brightness of the Hght which had been used in some of the 
tests, similar tests were made with weaker light. The re- 
sults were the same. I am therefore convinced that the 
animals did justice to their visual ability in these experiments. 

Finally, it seemed possible that looking directly at the 
source of light might be an unfavorable condition for color 
discrimination, and that a chamber flooded with colored light 
from above and from one end would prove more satisfactory. 



172 The Dancing Mouse 

To test this conjecture two thicknesses of blue glass were placed 
over one electric- box, two plates of green glass over the other ; 
the incandescent lamps were then fixed in such positions that 
the blue and the green within the two boxes appeared to the 
experimenter, as he viewed them from the position at which 
the mouse made its choice, of the same brightness. 

Mouse No. 2 was given two series of tests, series 18 and 
19, under these conditions, with the result that he showed 
absolutely no ability to tell the blue box from the green box. 
The opportunity was now taken to determine how quickly 
No. 2 would avail himself of any possibility of discriminating 
by means of brightness. With the blue at 21 candle meters, 
the green was increased to about 1800. Immediately dis- 
crimination appeared, and in the second series (22 of Table 
27) there were only two mistakes. 

The results of the blue-green experiments with light trans- 
mitted from in front of the animal and from above it are in 
entire agreement with those of the experiments in which 
reflected light was used. Since the range of intensities of 
illumination was sufficiently great to exclude the possibility 
of blinding and of under illumination, it is necessary to con- 
clude that the dancer does not possess blue-green vision. 

Again I must call attention to the fact that the behavior of 
the mice in these experiments is even more significant of their 
lack of discriminating ability than are the numerical results of 
the tables. After almost every series of tests, whether or not it 
came out numerically in favor of discrimination, I was forced to 
add thecomment, '-No satisfactory evidence of discrimination." 

We have now examined the results of green-red^^ green- 
blue, and blue-green tests. One other important combina- 
tion of the colors which were used in these experiments is 
possible, namely, b lue-re d. This is the most important of 
all the combinations in view of the results already described. 



The Sense of Sight : Color Vision 173 



for these colors represent the extremes of the visible spectrum, 
and might therefore be discriminable, even though those 
which are nearer together in the spectral series were not. 

As is shown by the results in Table 28, no combination of 
brightnesses rendered correct choice impossible in the case 

TABLE 28 
Blue-Red Tests 





Date 


Brightness Values 


Nc 


. 2 


No. 


20s 


Series 


Right 


Wrong 


Right 


Wrong 








(Blue) 


(Red) 


(Blue) 


(Red) 


I 


July 31 


1800 cm. on left 














24 cm. on right 


5 


5 


6 


4 


2 


Aug. I 


21 cm. on left 














1800 cm. on right 


6 


4 


6 


4 


3 


2 


i8cx) cm. on left 














21 cm. on right 


8 


2 


6 


4 


4 


3 


19 cm. on left 














1800 cm. on right 


9 


I 


6 


4 


5 


4 


1800 cm. on left 














7 cm. on right 


7 


3 


5 


5 


6 


5 


6 cm. on left 














1800 cm. on right 


10 





7 


3 


7 


6 


18 cm. on left 














74 cm. on right 


10 





9 


I 


8 


7 


1800 cm. on left 














7 cm. on right 


8 


2 


8 


2 


9 


8 


7 cm. on left 














1800 cm. on right 


7 


3 


8 


2 


10 


9 


Mixed values 














6 to 1800 cm. 


8 


2 


9 


I 


II 


10 


Blue 3 cm. 














Red 1800 cm. 


7 


3 


6 


4 



Brightness tests were now made, without the use of colors, 
iia 10 4655 



174 



The Dancing Mouse 
TABLE 28 — Continued 





Date 


Brightness Values 


No 


. 2 


No. 


205 


Series 


Right 
(Blue) 


Wrong 
(Red) 


Right 
(Blue) 


Wrong 
(Red) 


12 


10 


Blue 3 cm. 














Red 8 cm. 


4 


6 


6 


' 4 


13 


II 


Blue 3 cm. 










14 


13 


Red 7200 cm. 
Mixed values 


8 


2 


5 


5 


15 
16 


13 
14 


3 to 7200 cm. 

Same 

Blue 3 to 6 cm. 


7 

7 


3 
3 


7 
9 


3 

I 






Red 112 to 3650 cm. 


10 





10 






Series were now given to test the assumption that red appears dark 
to the dancer. 



17 


14 


Darkness on one side 














Red 3 cm. 


5 


5 


7 


3 


18 


14 


Blue 3 to 3650 cm. 














Red 3 to 3650 cm. 


10 





10 





19 


15 


Darkness on one side 














Red 3 cm. 


5 


5 


4 


6 


20 


15 


Blue 3 to 3650 cm. 














Red 3 to 3650 cm. 


10 





9 


I 


21 


16 


Darkness on one side 














Red 72 cm. 


5 


5 


7 


3 


22 


16 


Darkness on one side 














Red 1800 cm. 


6 


4 


10 






of the blue-red tests which are now to be described. Choice 
was extremely difficult at times, even more so perhaps than 
the table would lead one to suppose, and it is quite possible 
that color played no part in the discrimination. But that 
brightness difference in the colors was not responsible for 



The Sense of Sight: Color Vision 175 



r 

■ whatever success these mice attained in selecting the right 
P box is proved by the brightness-without-color series which 
follows series 11 of the table. Neither No. 2 nor No. 205 
showed preference for the lighter or the darker box. At 
the end of the sixteenth blue-red series, I was convinced that 
one of two conclusions must be drawn from the experiment : 
either the dancers possess a kind of blue-red vision, or red 
is of such a value for them that no brightness of visible green 
or blue precisely matches it. 

The latter possibility was further tested by an experiment 
whose results appear in series 17 to 22 inclusive, of Table 28. 
The conditions of series 17 were a brightness value of o in 
one box (darkness) and in the other red of a brightness of 
3 candle meters. Despite the fact that they had been per- 
fectly trained in blue-red tests to avoid the red, neither of 
the mice seemed able to discriminate the red from the dark- 
ness and to avoid it. This was followed by a series in which 
the brightness of both the blue and the red was varied be- 
tween 3 and 3650 candle meters, with the striking result that 
neither mouse made any mistakes. In series 19 red was 
used with darkness as in series 17, and again there was a 
total lack of discrimination. Series 20 was a repetition of 
series 18, with practically the same result. I then attempted 
to find out, by increasing the brightness of the red, how great 
must be its value in order that the dancers should distin- 
guish it readily from darkness. For the tests of series 21 it 
was made 72 candle meters, but discrimination did not 
clearly appear. At 1800 candle meters, as is shown in series 
22, the red was sufficiently different in appearance from 
total darkness to enable No. 205 to discriminate perfectly 
between the two electric-boxes. For No. 2 discrimination 
was more difficult, but there was no doubt about his ability. 
It would appear from these tests that the dancers had not 



176 



The Dartcing Mouse 



learned to avoid red. Therefore we are still confronted with 
the question, can they see colors? 

The account of my color vision experiments is finished. 
If it be objected that other than visual conditions may ac- 
count for whatever measure of discriminating ability, apart 
from brightness discrimination, appears in some of the series, 

TABLE 29 

Visual Check Tests 
With the Electric -boxes Precisely Alike Visually 



Series 


Date 


No. 151 


No. 152 


Right 


Wrong 


Right 


Wrong 


I 
2 

3 
4 
5 
6 

7 
8 

9 
10 


Sept. 29 
30 
Oct. I 
2 
3 
4 
5 
6 

7 
8 


6 

5 
3 
5 
3 
6 

5 


4 
5 
7 
5 
7 
4 
5 


4 
6 

4 
3 
5 
5 
5 
3 
6 

4 


6 

4 
6 

7 
5 
5 
5 
7 
4 
6 


Averages 


4.7 


5-3 


4.5 


5-5 



the results of the series of Table 29, in which all conceivable 
visual means of discrimination were purposely excluded, and 
those of the several check tests which have been described 
from time to time in the foregoing account, should furnish a 
satisfactory and definite answer. I am satisfied that what- 
ever discrimination occurred was due to vision; whether we 
are justified in calling it color vision is quite another question. 
I conclude from my experimental study of vision that 
although the dancer does not possess a color sense like ours. 



The Sense of Sight: Color Vision 177 

it probably discriminates the colors of the red end of the J 
spectrum from those of other regions by difference in the 
stimulating value of light of different wave lengths, that 
such specific stimulating value is radically different in nature 
from the value of different wave lengths for the human eye, 
and that the red of the spectrum has a very low stimulating 
value for the dancer. In the light of these experiments we 
may safely conclude that many, if not most, of the tests of 
color vision in animals which have been made heretofore by 
other investigators have failed to touch the real problem 
because the possibility of brightness discrimination was not 
excluded. 

Under the direction of Professor G. H. Parker, Doctor 
Karl Waugh has examined the structure of the retina of the 
dancing mouse for me, with the result that only a single 
type of retinal element was discovered. Apparently the 
animals possess rod-like cells, but nothing closely similar to 
the cones of the typical mammalian retina. This is of 
peculiar interest and importance in connection with the re- 
sults which I have reported in the foregoing pages, because 
the rods are supposed to have to do with brightness or 
luminosity vision and the cones with color vision. In fact, 
it is usually supposed that the absence of cones in the mam- 
mahan retina indicates the lack of color vision. That this 
inference of functional facts from structural conditions is 
correct I am by no means certain, but at any rate all of the 
experiments which I have made to determine the visual 
ability of the dancer go to show that color vision, if it exists 
at all, is extremely poor. It is gratifying indeed to learn, 
after such a study of behavior as has just been described, 
that the structural conditions, so far as we are able to judge 
at present, justify the conclusions which have been drawn. 



CHAPTER XI 
The Role of Sight in the Daily Life of the Dancer 

Darting hither and thither in its cage, whirling rapidly, 
now to the left, now to the right, running in circles, passing 
through holes in the nest box quickly and neatly, the dancer, 
it would seem, must have excellent sight. But careful obser- 
vation of its behavior modifies this inference. For it appears 
that a pair of mice dancing together, or near one another, 
sometimes collide, and that it is only those holes with which 
the animal is familiar that are entered skillfully. In fact, 
the longer one observes the behavior of the dancer under 
natural conditions, the more he comes to believe in the im- 
portance of touch, and motor tendencies. Sight, which at 
first appears to be the chief guiding sense, comes to take a 
secondary place. In this chapter it is my purpose to show 
by means of simple experiments what part sight plays in the 
dancer's life of habit formation. 

The evidence on this subject has been obtained from four 
sources: (i) observation of the behavior of dancers in their 
cages; (2) observation of their behavior when bhnded; 
(3) observation of their behavior in a great variety of dis- 
crimination experiments, many of which have already been 
described ; and (4) observation of their behavior in labyrinth 
experiments which were especially planned to exhibit the im- 
portance of the several kinds of vision which the dancer 
might be supposed to possess. The evidence from the first 
three of these sources may be presented summarily, for much 

178 



Role of Sight in Daily Life of Dancer 179 

of it has already appeared in earlier chapters. That from 
the fourth source will constitute the bulk of the material of 
this chapter. 

My observation of the behavior of the mice has furnished 
conclusive evidence of their ability to see moving objects. 
But that they do not see very distinctly, and that they do 
not have accurate perception of the form of objects, are 
conclusions which are supported by observations that I have 
made under both natural and experimental conditions. In 
Chapters VII, VIII, IX, and X, I have presented an abun- 
dance of evidence of brightness vision and, in addition, indica- 
tions of a specific sensitiveness to wave length which may be 
said to correspond to our color vision. It is noteworthy, 
however, that all of the experimental proofs of visual ability 
were obtained as the result of long periods of training. Sel- 
dom, indeed, in my experience with them, have the dancers 
under natural conditions exhibited forms of activity which 
were unquestionably guided by vision. 

It is claimed by tliose who have experimented with blinded 
dancers that the loss of sight decreases the amount and 
rapidity of movement, and the ability of the animals to avoid 
obstacles. 

By means of the discrimination method previously used in 
the preHminary experiments on color vision, a full descrip- 
tion of which may be found in Chapter IX, p. 133, the 
dancers' ability to perceive form was tested. Immediately 
after the two males A and B had been given the "food-box" 
tests, whose results appear in Table 15, they were tested in 
the same apparatus and by the same method for their ability 
to discriminate a rectangular food-box from a round one. 
In the case of the color discrimination tests, it will be remem- 
bered that the circular tin boxes 5 cm. in diameter by 1.5 cm. 
in depth, one of which was covered with blue paper, the 



i8o 



The Dajicing Mouse 



other with orange, were used. For the form discrimination 
tests I used instead one of the circular boxes of the dimen- 
sions given above and a rectangular box 8.5 cm. long, 5.5 cm. 
wide and 2.5 cm. deep. ^' Force" was placed in the circular 
box. The tests were given, in series of 20, daily. 

The results of 15 series of these tests, as may be seen by 
the examination of Table 30, are about as definitely nega- 
tive, so far as form discrimination is in question, as they 
possibly could be. From the first series to the last there is 
not one which justifies the inference that either of the dancers 

TABLE 30 
Visual Form Tests 





Date 


Mouse A 


Mouse B 


Series 


Right 


Wrong 


Right 


Wrong 






(Circular 
Box) 


(Rectangu- 
lar Box) 


(Circular 
Box) 


(Rectangu- 
lar Box) 


I 


Jan. 5 


10 


10 


9 


II 


2 


7 


12 


8 


13 


7 


3 


10 


6 


14 


10 


10 


4 


n 


^ 7 


13 


10 


10 


5 


12 


9 


II 


10 


10 


6 


13 


II 


9 


II 


9 


7 


14 


13 . 


7 


9 


II 


8 


15 


10 


10 


II 


9 


9 


16 


10 


10 


II 


9 


10 


17 


II 


9 


9 


II 


II 


18 


II 


9 


12 


8 


12 


19 


12 


8 


10 


10 


13 


20 


10 


10 


12 


8 


14 


21 


10 


10 


8 


12 


15 


22 


10 


10 


10 


10 


Totals 


152 


148 


155 


145 



I 



Role of Sight in Daily Life of Dancer i8i 

depended upon the form of the boxes in making its choice. 
In view of the general criticisms I have made concerning 
the use of hunger as a motive in experiments on animal 
behavior, and in view of the particular criticisms of this very 
method of testing the discriminating powers of the mouse, it 
may seem strange that space should be given to a report of 
these tests. I sympathize with the feeling, if any one has it, 
but, at the same time, I wish to call attention to the fact 
that almost any mammal which is capable of profiting by 
experience, and which, under the same conditions, could dis- 
tinguish the rectangular box from the circular one, would 
have chosen the right box with increasing accuracy as the 
result of such experience. The results are important in my 
opinion, not because they either prove or disprove the ability 
of the dancer to discriminate these particular forms, the dis- 
crimination of which might fairly be expected of any animal 
with an image-forming eye, but because they demonstrate 
an important characteristic of the dancing mouse, namely, its 
indifference to the straightforward or direct way of doing 
things. 

Most mammals which have been experimentally studied 
have proved their eagerness and ability to learn the shortest, 
quickest, and simplest route to food without the additional 
spur of punishment for wandering. With the dancer it is 
different. It is content to be moving; whether the movement 
carries it directly towards the food is of secondary impor- 
tance. On its way to the food-box, no matter whether the 
box be slightly or strikingly different from its companion 
box, the dancer may go by way of the wrong box, may take 
a few turns, cut some figure-eights, or even spin like a top 
for seconds almost within vibrissa-reach of the food-box, 
and all this even though it be very hungry. Activity is pre- 
eminently important in the dancer's life. 



1 82 The Dancing Mouse 

In passing I may emphasize the importance of the fact 
that at no time did the brightness or color discrimination 
tests furnish evidence of attempts on the part of the dancers 
to choose by means of sHght differences in the form of the 
cardboards or the cardboard carriers. Several times form 
differences, which were easily perceivable by the human sub- 
ject, were introduced in order to discover whether the mice 
would detect them and learn to discriminate thereby instead 




Figure 22. — Cards used for tests of form discrimination. 

of by the visual conditions of brightness or color. As these 
experiments failed to furnish evidences of form discrimina- 
tion, the following special test in the discrimination box was 
devised. 

The color discrimination box of Chapter X was arranged 
so that the light at the entrance to each electric-box had a 
value of 20 candle meters, less the diminution caused by a 
piece of ground glass which was placed over the end of the 
electric-boxes to diffuse the light. The windows through 
which the light entered the electric-boxes were covered with 
pieces of black cardboard ; in one of these cardboards I had 
cut a circular opening 4 cm. in diameter, and in the other 
an opening of the same area but markedly different shape. 



Role of Sight in Daily Life of Dancer 183 

These openings are shown in Figure 22. As the mouse ap- 
proached the entrance to the electric-boxes, it was confronted 
by these two equally illuminated areas, whose chief differ- 
ence was one of form. Difference in the amount of light 
within the boxes was excluded so far as possible. The ques- 
tion which I asked was, can the dancer discriminate by 
means of this difference in visual form? 

For the purpose of settling this point and of gaining ad- 
ditional knowledge of the role of vision, two individuals were 
tested in the discrimination box under the conditions which 
have just been described. During the first ten days of the 
experiment each of these mice, Nos. 420 and 425, was given 
a series of ten tests daily. At the end of this period experi- 
mentation with No. 425 had to be discontinued, and the 
number of daily tests given to No. 420 was increased to 
twenty. 

Instead of taking space for the presentation of the daily 
records, I may state the general results of the tests. Neither 
of the mice learned to choose the right box by means of form 
discrimination. In fact, there was absolutely no sign of dis- 
crimination at any time during the tests. This result is as 
surprising as it is interesting. I could not at first believe 
that the mice were unable to perceive the difference in the 
lighted areas, but assumed that they were prevented from 
getting the outlines of the areas by the blinding effect of the 
light. However, decreasing the intensity of the illumination 
did not alter the result. According to the indications of this 
experiment, the dancer's ability to perceive v isual form is 
extremely, poor. 

Thus far the purpose of our experiments has been to ascer- 
tain what the dancer is enabled to do by sight. Suppose we 
now approach the problem of the role of this sense by try- 
ing to find out what it can do without sight. 






184 The Dancing Mouse 

For the investigation of this matter the labyrinth method 
seemed eminently suitable. The first form of labyrinth 
which was used in these visual tests appears in ground 
plan in Figure 23. It was made of ij cm. boards. The 
length was 52 cm., the width 17 cm., the depth 10 cm. Each 
of the doorways, I (the entrance), i, 2, 3, and O (the exit), 
was 5 by 5 cm. The alleys were 2 J cm. wide. For this 







3 





<> 







Figure 23. — Labyrinth B. 7, entrance; O, exit; i, 2, 3, doorways between alleys. 

width the necessity is obvious from what has already been 
said of the animal's propensity to whirl on all occasions. As 
the mice almost never tried to climb up the walls, no cover 
for the labyrinth was needed. The direct route is indicated 
by the symbols /-1-2-3-O. If an error be defined as a choice 
of the wrong path as the animal progressed toward the exit, 
five mistakes were possible in the forward course : the first by 
turning to the left at the entrance ; the second by faihng to 
pass through doorway i ; the third by turning to the right 
after passing through doorway i ; the fourth by failing to 
pass through doorway 3, and the fifth by turning to the left 
after passing through 3. In case the mouse retraced its 
course, any mistakes made as it again progressed towards O 
were counted, as at first, no matter how many times it 



Role of Sight in Daily Life of Dancer 185 

went over the same ground. Thus an individual might make 
the same mistake several times in the course of a single test 
in the labyrinth. 

With this labyrinth Nos. 7, 998, 15, 16, 151, and 152 were 
tested. At first a record was kept of the time which elapsed 
from the instant the animal entered / to the instant it emerged 
at O, of the path which it followed, and of the number of 
errors which it made ; but later only the number of errors 
was recorded. 

TABLE 31 

The Role of Sight 







Labyrinth-B Experiments 








No 


• 7 


No. 998 


Test 




Time 


Errors 


Time 


Errors 


I 


June 16 


66'' 


8 


127- 


19 


2 


16 


II 





94 


12 


3 


16 


15 


2 


18 


3 


4 


16 


7 





13 


2 


5 


16 


5 





10 




6 


18 


61 


15 


12 




7 


18 


13 


3 


14 




8 


18 


14 


5 


8 




9 


18 


24 


9 


16 




10 


18 


10 


I 


9 




i " 


19 


36 


13 


80 


17 


r 12 


19 


8 


3 


10 




13 


19 


6 


I 


7 




14 


19 


9 


I 


8 





15 


19 


12 


2 


7 





16 


20 


14 


I 


25 





17 


20 


28 


3 






18 


20 


No efforts 


to escape 


No efforts to escape 



i86 



The Dancing Mouse 



TABLE 32 
Labyrinth-B Experiments 
with 
Electric Shock given as Punishment for Mistakes 







No 


7 


No. 998 


Test 


Date 














Condition 


Errors 


Condition 


Errors 


I 


June 29 


Light 


4 


Light 


9 


2 


29 


Light 


I 


Light 


3 


3 


29 


Light 


I 


Light 


2 


4 


29 


Light 





Light 





5 


29 


Light 





Light 





6 


29 


Light 





Light 





' 7 


29 


Light 


I 


Light 





8 


29 


Light 





Light 





9 


29 


Light 


I 


Darkness 





10 


29 


Light 


I 


Light 





II 


29 


Light 


I 


Darkness 





12 


29 


Light 





Light 





13 


29 


Light 





Light 





14 


29 


Light 





Light 





15 


29 


Light 





Light 





16 


29 


Light 





Light 





17 


29 


Darkness 


2 


Darkness 





18 


29 


Light 


2 


Light with 
paper 





19 


29 


Light 





Light 





20 


29 


Darkness 





Light with 
paper 





21 


29 


Light 





Light 





22 


29 


Light 





Darkness 





23 


29 


Light 





Odorless 






Role of Sight in Daily Life of Dancer 187 
TABLE 32 — Continued 







No 


7 


No. 998 


Test 


Date 














Condition 


Errors 


Condition 


Errors 


24 


June 29 


Light 





Darkness 





25 


29 


Light 









26 


29 


Darkness 


4 






27 


29 


Light with 
paper 


I 






28 


29 


Light 









29 


29 


Light with 
paper 


I 






30 


29 


Darkness 









31 


29 


Odorless 


2 






32 


29 


Darkness 


4 







As the results in Table 31 show, the time and number of 
errors rapidly diminished. Number 7, for example, made no 
errors in the second test. The chiefly significant fact which 
appeared in these preliminary experiments, however, was that 
the mice soon ceased to care whether they got out of the 
labyrinth or not. After they knew the path perfectly, they 
would enter the wrong passages repeatedly and wander about 
indefinitely. It was obvious, therefore, that the labyrinth 
could not be used to reveal the role of sight unless some 
sufficiently strong motive for continuous effort to escape from 
it could be discovered. Naturally I looked to the electric 
shock for aid. 

The labyrinth of Figure 23, which for convenience in dis- 
tinguishing it from several other forms to be described later 
I have designated as labyrinth B, was placed upon a board 
90 cm. long and 30 cm. wide about which had been wound 
two pieces of phosphor bronze wire after the manner de- 



1 88 



The Dancing Mouse 



N 




Figure 24. — Labyrinth B on 
an interrupted circuit board. 7- 
1-2-3-O, labyrinth path; B, nest- 
box; AT, nest; EW , board wound 
with phosphor bronze wire; IC, 
induction apparatus; C, electric 
cell; K, key. 



scribed on p. 94. At O, Figure 
24, there was an opening closed by 
a swinging door which led into 
a box 40 by 24 cm. In one 
corner of this box was a small 
nest-box. The significance of this 
rearrangement of the labyrinth is 
apparent. As in the preliminary 
tests, the dancer was started at I, 
but instead of being allowed to 
wander about without any other 
result than delay in escape, it was 
given a shock each time it made 
an error. The satisfaction of 
escaping from the narrow bounds 
of the labyrinth's passages, which 
alone was not strong enough to 
impel a dancer constantly to do 
its best to escape, was thus sup- 
plemented by the powerful and all- 
controlling tendency to avoid the 
disagreeable stimulus which re- 
sulted from entering certain of the 
passages. The result of this modi- 
fication of method is strikingly ex- 
hibited by the data of Table 32. 
This table was constructed for 
the purpose of exhibiting the prin- 
cipal features of the results ob- 
tained with labyrinth B in certain 
preliminary experiments in which 
the conditions were changed in 
various ways. Chief among the 



Role of Sight in Daily Life of Dancer 189 

important facts which appear in the illustrative data (for Nos. 
7 and 998) which are presented, are the following. The dancers 
readily learn the path of labyrinth B so that they can follow 
it quickly and with perfect accuracy. After familiarity with 
the direct path from entrance to exit has been gained, they 
become indifferent about escaping and tend to wander aim- 
lessly. The introduction of the electric shock as punish- 
ment for the choice of the wrong passage impels them to do 
their best to avoid errors. The path once learned can be 
followed in total darkness with few or no errors. Table 32 
indicates marked differences in the behavior of No. 7 and 
No. 998. The latter learned the path readily and was httle 
disturbed by any of the changes in conditions. In total 
darkness he followed the path rapidly and accurately, as 
was indicated by the time of the trip and the path that he 
left on a sheet of smoked paper that had been placed on the 
floor of the labyrinth as a means of obtaining a record of the 
errors made. The presence of the smoked paper did not 
seem to interfere at all with his behavior, nor did the thorough 
washing of the labyrinth and the resultant removal of its 
odors. In the case of No. 7 the opposite was true. She 
did not learn the path readily, was confused by any change 
in conditions, had great difficulty in finding her way in dark- 
ness, made errors when the smoked paper was placed on 
the floor and after the odors of the labyrinth had been re- 
moved by washing. Of the six dancers which were observed 
in these preliminary tests, No. 7 alone gave convincing evi- 
dence of the importance of sight. 

I think we may say in the light of the results of the table 
that such errors as appear in the darkness tests are due 
rather to the disturbing influence of a change in the condi- 
tions of the experiment than to the exclusion of visual data, 
for as many or more errors were sometimes caused simply by 



190 The Dancing Mouse 

changing the position of the labyrinth, placing smoked paper 
on the floor, or by introducing a new odor at some point. 
The exclusion of the possibility of guidance by smell and 
touch did not seriously interfere with the animal's ability to 
follow the path. 

The results which have just been considered seemed to be 
of sufficient interest and importance to justify the further use 
of the labyrinth method in the investigation of the role of 
vision. A series of experiments with labyrinth B was there- 
fore planned so that the im.portance of sight, touch, and 
smell in connection with this form of habit should be more 
satisfactorily exhibited. Does the dancer follow the path by 
sight, touch, smell, by all, or by no one of them? 

This series of tests with labyrinth B, whose several pur- 
poses may best be explained in connection with the various 
kinds of tests enumerated below, consisted of : 

I. A preliminary test in which the dancer was permitted 
to wander about in the labyrinth, without being shocked, 
until it finally escaped to the nest-box by way of the exit. 
Thus the animal was given an opportunity to discover that 
escape from the maze was possible. 

II. This was immediately followed by a series of tests at 
the rate of about one per minute, with an electric shock as 
punishment for every mistake. This was continued without 
interruption until the path had been followed without error 
five times in succession. 

III. The labyrinth was now moved about 3 cm. to one 
side so that it covered a new floor area, and a test was given 
for the purpose of ascertaining whether the mouse had been 
following a trail on the floor. 

IV. Tests with smoked paper on the floor were now 
alternated with tests in which the floor was plain. The 
alternation was rendered necessary by the fact that the paper 



Role of Sight i7i Daily Life of Dancer 191 

was laid over the electric wires and therefore prevented the 
punishment of mistakes. The purpose of these tests was to 
discover whether the smoked paper, which was an essential 
condition for the next test, was itself a disturbing condition. 
These tests were continued until the animal had followed the 
path correctly, despite the smoked paper, twice in succession. 

V. The electric lights were now turned out and tests were 
given in total darkness, with smoked paper on the floor as a 
means of obtaining a record of the number of errors. These 
tests were continued until the path had been followed once 
correctly. 

VI. The labyrinth was now thoroughly washed with warm 
water, to which a little kerosene had been added, and quickly 
dried over a steam radiator. This usually necessitated a 
delay of about five minutes. As soon as the labyrinth was 
dry, tests were given to discover whether the odors of the 
various passages had been serving as important guiding 
conditions. These tests were continued until the path had 
been followed once without error. 

VII. A final test in darkness completed the series. 

As it was not possible for the observer to watch the ani- 
mal and thus to count the number of mistakes which it made 
in total darkness, the simple method of placing a piece of 
smoked paper on the floor of the labyrinth was used. The 
mouse left a graphic record of its path "on the paper and 
from this the number of errors could be ascertained. In 
the tests now to be described the smoked paper was placed 
upon the electric wires, but later a form of electric labyrinth 
was devised in which it was underneath and therefore did 
not interfere with the electric shock. 

The above series of tests was given under the same external 
conditions in a dark-room to six pairs of dancers. In all 
cases, two individuals, a male and a female, which had been 



192 



The Dancing Mouse 



kept in the same cage, were experimented with at the same 
time, i.e. one was permitted to rest in the nest-box while 
the other was being put through a test. This was done in 
order that the comparison of the resuhs for males and 
females should be perfectly fair. 

The detailed results of this long series of tests may be 
presented for only two individuals, Nos. 210 and 215, Table 
33. In this table lines separate the results of the seven 
different kinds of tests. 



TABLE 33 
The Role of Sight, Touch, and Smell in Labyrinth Experiments 



No. 210 


No. 215 




Test 


Condition 


Errors 


Condition 


Errors 


I. I 


No shock 


9 


I. No shock 


2 


11. 2 


Shock 


5 


II. Shock 


3 


3 


Shock 


4 


Shock 


I 


4 


Shock 


2 


Shock 





5 


Shock 


3 


Shock 





6 


Shock 





Shock 





7 


Shock 





Shock 





8 


Shock 
Shock 
Shock 







Shock 





9 


III. Labyrinth moved 





10 


IV. Paper on floor 
No pap^r (shock) 
Paper 


4 


III. II 


Labyrinth moved 








IV. 12 


Paper on floor 


2 





13 


No paper (shock) 





No paper 





14 


Paper 


I 


Paper 


I 


IS 


No paper 





No paper 





16 


Paper 


7 


Paper 


4 


17 


No paper 





No paper 





18 


Paper 





Paper 






Role of Sight in Daily Life of Dancer 193 
TABLE 33 — Continued 



No. 210 


No. 215 


Test 


Condition 


Errors 


Condition 


Errors 


19 

20 
21 


No paper 
Paper 
No paper 
Paper 
No paper 
Paper 
No paper 
Paper 
No paper 
Paper 
No paper 




4 

2 
2 
I 







No paper 
Paper 
No paper 







22 


V. Darkness 





23 
24 


VL Labyrinth washed 


2 




25 
26 

27 
28 

29 


VIL Darkness 


2 


V. 30 


Darkness 







VL 31 

32 


Labyrinth washed 


2 





VIL 33 


Darkness 








The average results for the twelve individuals (six of each 
sex) which were subjected to the tests, I have arranged in 
Table 34. The Roman numerals at the top of the table 
designate the seven groups of tests, and the figures under 
each, the numerical results of the tests. I may explain and 
comment upon the averages of the several columns of this 
table in turn. 

Column I gives the number of errors made in the pre- 
Hminary test. Curiously enough, the males made many 
more errors than the females. 

For the second group of tests (II) two results have been 
tabulated : the number of the first correct test, and the total 
number of tests before the path was followed correctly five 



194 



The Dancing Mouse 



times in succession. The first correct trip came usually 
after not more than five or six tests, but five successive 
correct trips demanded on the average at least fourteen 
training tests. 

Destruction of the floor path by movement of the laby- 
rinth to one side, v^ithout changing its relations to the points 
of the compass, disturbed the mice very Httle. Only four of 
the twelve individuals made any mistakes as a result of the 
change in the tactual conditions, and the average error as it 
appears in Column III is only .3. 



TABLE 34 
Role of Sight, Touch, and Smell in Labyrinth Experiments 



Females 



Males 


I. 

Preliminary 

Test. 

Errors 


n. 

Training Tests. 

No. OF Tests Before 

Correct 


ni. 

Labyrinth 
Moved. 
Errors 


IV. 

Smoked 

Paper on 

Floor. 

No. of Times 




First Time 


Five Times 


Before Cor- 
rect Twice 


210 
212 
214 
220 
410 
420 


9 
2 
6 

25 
II 

14 


5 

3 
10 

4 
6 
6 


9 
8 

28 

8 

20 

. 14 




I 




I 


9 

3 

22 

14 
10 

7 


Averages 


II. 2 


5-7 


14-5 


.3 1 10.8 



211 


16 


6 


10 


I 


5 


213 


7. 


5 


14 


I 


21 


215 


2 


3 


7 





6 


225 


14 


6 


18 





14 


415 


6 


6 


13 





3 


425 


10 


7 


13 





8 


Averages 


9.2 


5-5 


12.5 


•3 


9-5 



Role of Sight in Daily Life of Da^icer 195 
TABLE 34 — Continued 





V. 

Darkness 


VI. 

Labyrinth 
Washed. 
Errors 


VII. 

Darkness. 
Errors 




Errors in 
First Test 


No. OF Tests 
Before Cor'ct 


210 

212 
214 
220 
410 
420 



2 

2 

I 
2 


I 
2 

I 

4 
3 
4 


2 



2 
2 

I 







I 
4 


Averages 


1.2 [ 2.5 1 1.2 


0.8 



Females 



211 


2 


2 








213 


2 


2 


— 


3 


215 





I 


2 


2 


225 


3 


2 








415 


I 


3 


2 


I 


425 


I 


7 








Averages 


1-5 


2.8 


0.7 


I.O 



That covering the floor v^ith smoked paper forced the mice 
to relearn the path, in large measure, is evident from the 
results of Colurmi IV. An average of ten tests v^as necessary 
to enable the mice to follow the path correctly. It is almost 
certain, however, that the interference with the perfectly 
formed labyrinth habit which this change in the condition 
of the floor 'caused was not due to the removal of impor- 
tant tactual sense data. 

As Column V shows, the number of errors in total dark- 
ness is very small. Some individuals gave no sign of being 
disturbed by the absence of visual guidance, others at first 
seemed confused. I have given in the table the number of 



196 The Dancing Mouse 

errors in the first darkness test and the number of the first 
test in which no mistakes occurred. 

No more disturbance of the dancer's abiHty to follow the 
path which it had learned resulted from washing the labyrinth 
thoroughly than from darkening the room. Indeed it is clear 
from Column VI that the path was not followed by the use of 
smell. However, the test in darkness, after the odor of the 
box had been removed, proved conclusively that in most 
cases the mice could follow the path correctly without visual 
or olfactory guidance. 

The behavior of 18 individuals as it was observed in laby- 
rinth B makes perfectly evident three important facts, (i) In 
following the path which it has learned, the dancer in most 
instances is not guided to any considerable extent by a trail 
(odor or touch) which has been formed by its previous 
journeys over the route; (2) sight is quite unnecessary for 
the easy and perfect execution of the labyrinth habit, for even 
those individuals which are at first confused by the darken- 
ing of the experiment room are able after a few tests to follow 
the path correctly; (3) and, finally, smell, which according to 
current opinion is the chiefly important sense of mice and rats, 
is not needful for the performance of this habitual act. 

At this point we may very fittingly ask, what sense data 
are necessary for the guidance of the series of acts which 
constitutes the labyrinth habit? I answer, probably none. 
A habit once formed, the senses have done their part ; hence- 
forth it is a motor process, whose initiation is conditioned 
by the activity of a receptive organ (at times a sense receptor), 
but whose form is not necessarily dependent upon immediate 
impressions from eye, nose, vibrissae, or even from internal 
receptors. These are statements of my opinion; whether 
they express the truth, either wholly or in part, only further 
experimentation can decide. 



Role of Sight in Daily Life of Daitcer 197 

In considering the results of these labyrinth tests it is im- 
portant that we distinguish clearly those which have to do 
with the conditions of habit formation from those which in- 
stead have to do with the conditions of habit performance. 
Ssnse data which are absolutely necessary for the learning of 
a labyrinth path may be of little or no importance for the 
execution of the act of following the path after the learning 
process has been completed. Thus far in connection with 
the labyrinth tests we have discussed only the relations of 
sight, touch, and smell to what I have called habit per- 
formance. We may now ask what part these senses play in 
the formation of a labyrinth habit. 

A very definite answer to this question is furnished by 
observation of the behavior of the dancers in the tests. Most 
of them continuously made use of their eyes, their noses, and 
their vibrissae. Some individuals used one form of receptive 
organ almost exclusively. I frequently noticed that those 
individuals which touched and smelled of the labyrinth 
passages most carefully gave least evidence of the use of 
sight. It is safe to say, then, that under ordinary conditions 
habit formation in the dancer is conditioned by the use of 
sight, touch, and smell, but that these senses are of extremely 
different degrees of importance in different individuals. And 
further, that, although in the case of some individuals the loss 
of sight would not noticeably delay habit formation, in the 
case of others it would seriously interfere with the process. 
When deprived of one sense, the dancer depends upon its 
remaining channels of communication with environment. 
Indeed there are many reasons for inferring that if deprived 
of sight, touch, and smell it would still be able to learn a 
labyrinth path; and there are reasonable grounds for the 
belief that a habit once formed can be executed in the absence 
of all special sense data. Apparently the various receptive 



198 The Dancing Mouse 

organs of the body furnish the dancer with impressions which 
serve as guides to action and facihtate habit formation, 
although they are not necessary for habit performance. 

The reader may wonder why I have not carried out sys- 
tematic experiments to determine accurately and quantita- 
tively the part which each sense plays in the formation of a 
labyrinth habit instead of basing my inferences upon inci- 
dental observation of the behavior of the dancers. The 
reason is simply this : the number and variety of experiments 
which were suggested by the several directions in which this 
investigation developed rendered the performance of all of 
them impossible. I have chosen to devote my time to other 
lines of experimentation because a very thorough study of 
the conditions of habit formation has recently been made 
by Doctor Watson.^ 

What is the role of sight in the dancing mouse? How 
shall we answer the question ? The evidence which has been 
obtained in the course of my study of the animal indicates 
that brightness vision is fairly acute, that color vision is poor, 
that although form is not clearly perceived, movement is 
readily perceived. My observations under natural conditions 
justify the conclusion that sight is not of very great impor- 
tance in the daily life of the dancer, and my observations 
under experimental conditions strongly suggest the further 
conclusion that movement and changes in brightness are the 
only visual conditions which to any considerable extent con- 
trol the activity of the animal. 

^ Watson, J. B., Psychological Review, Monograph Supplement, Vol. 8, No. 2, 
1907. 



CHAPTER XII 
Educability: Methods of Learning 

Nearly all of the experiments described in earlier chap- 
ters have revealed facts concerning the educability of the 
dancer. In order to supplement the knowledge of this sub- 
ject thus incidentally gained and to discover the principles of 
educability, the specially devised experiments whose results 
appear in this and succeeding chapters were arranged and 
carried out with a large number of mice. In the work on the 
modifiability of behavior I have attempted to determine (i) by 
what methods the dancer is capable of profiting by experience, 
(2) the degree of rapidity of learning, (3) the permanency of 
changes wrought in behavior, (4) the effect of one kind of train- 
ing upon others, (5) the relation of re-training to training, and 
(6) the relation of all these matters to age, sex, and individuality. 

As it is obvious that knowledge of these subjects is a 
necessary condition for the intelligent appreciation of the 
capacities of an animal, as well as of the choice of methods by 
which it may be trained advantageously, perhaps it is not too 
much to expect that this investigation of the nature and con- 
ditions of educability in the dancing mouse may give us some 
new insight into the significance of certain aspects of human 
education and may serve to suggest ways in which we may 
measure and increase the efficiency of our educational methods. 

Merely for the sake of convenience of description I shall 
classify the methods which have been employed as problem 
methods, labyrinth methods, and discrimination methods. 
That these names are not wholly appropriate is suggested by 

199 



200 The Dancing Mouse 

the fact that discrimination necessarily occurs in connection 
with each of them. As problem methods we may designate 
those tests of initiative and modifiability which involve the 
opening of doors by pushing or pulling them, and the climb- 
ing of an inclined ladder. An example of the labyrinth 
method has been presented in Chapter XI. The name dis- 
crimination method I have applied to those tests which in- 
volve the choice of one of two visual, tactual, or olfactory 
conditions. The white-black discrimination tests, for ex- 
ample, served to reveal the rapidity and permanency of 
learning as well as the presence of brightness vision. 

In the case of most mammals whose educability has been 
studied experimentally, problem methods have proved to be 
excellent tests of docility and initiative. The cat, the rac- 
coon, the monkey, in their attempts to obtain food, learn to 
pull strings, turn buttons, press latches, slide bolts, pull 
plugs, step on levers. The dancer does none of these things 
readily. Are we therefore to infer that it is less intelligent, 
that it is less docile, than the cat, the raccoon, or the monkey? 
Not necessarily, for it is possible that these methods do not 
suit the capacity of the animal. As a matter of fact, all of 
the tests which are now to be described in their relation to 
the educability of the dancer bear witness to the importance 
of the selection of methods in the light of the motor equip- 
ment and the habits of the animal which is to be tested. 
Judged by ordinary standards, on the basis of results which 
it yields in problem and labyrinth tests, the dancer is ex- 
tremely stupid. But that this conclusion is not justified is 
apparent when it is judged in the light of tests which are 
especially adapted to its peculiarities. 

Problems which are easy for other mammals because of 
their energetic and persistent efforts to secure food in any 
way which their motor capacity makes possible are useless 



Educability : Methods of Learning 201 

as tests of the dancer's abilities, because it is not accustomed 
to obtain its food as the resuU of strenuous and varied activi- 
ties. There are problems and problems; a condition or 
situation which presents a problem to one organism may 
utterly lack interest for an organism of different structure 
and behavior. What is a problem test in the case of the cat 
or even of the common mouse, is not necessarily a problem 
for the dancer. Similarly, in connection with the labyrinth 
method, it is clear that the value of the test depends upon 
the desire of the organism to escape from the maze. The 
cat, the rat, the tortoise do their best to escape ; the dancer 
is indifferent. Clearly, then, methods of training should be 
chosen on the basis of a knowledge of the characteristics of 
the animal whose educability is to be investigated. 

The simplest possible test of the intelligence of the dancer 
which I could devise was the following. Beside the cage in 
which the mice were kept I placed a wooden box 26 cm. long, 
23 cm. wide, and 12 cm. deep. Neither this box nor the 
cage was covered, for the animals did not attempt to climb 
out. As a way of passing from one of these boxes to the 
other I arranged a ladder made of wire fly-screen netting. 
This ladder was about 8 cm. broad and it extended from the 
middle of one side of the wooden box upward at an angle 
of about 30° to the edge of the box and then descended at 
the same angle into the cage. 

A dancer when taken from the nest-box and placed in the 
wooden box could return to its cage and thus find warmth, 
food, and company by climbing the ladder. It was my aim 
to determine; by means of this apparatus, whether the 
dancers can learn such a simple way of escape and whether 
they learn by watching one another. As it turned out, a 
third value belonged to the tests, in that they were used also 
to test the influence of putting the mice through the act. 



202 The Dancing Mouse 

In the first experiment three dancers, Nos. looo, 2, and 6, 
were together placed in the wooden box. At the end of 15 
minutes not one of them had succeeded in returning to the 
cage. They were then driven to the bottom of the ladder 
and started upward by the experimenter ; with this assistance 
all escaped to the nest-box. At the expiration of 5 minutes 
they were again placed in the wooden box, whence the chilly 
temperature (about 60° F.) and the lack of food made 
them eager to return to their cage. No attempt to climb up 
the ladder was made by any of them within 15 minutes, so 
the experimenter directed them to the ladder and started 
them upward as in the first test. This completed the experi- 
ment for the day. The following day two tests were given 
in the same way. In the second of these tests, that is, on its 
fourth trial, No. 1000 climbed over of his own initiative in 
5 minutes. The others had to be assisted as formerly. On 
the third day No. 1000 found his way back to the nest-box 
quickly and fairly directly, but neither No. 2 or No. 6 climbed 
of its own initiative in the first test. When their movements 
were restricted to the region of the box about the base of the 
ladder, both of them returned to the cage quickly. And on 
the second test of the third day all the mice climbed the 
ladder directly. 

In Table 35 I have given the time required for escape in 
the case of 40 tests which were given to these 3 individuals 
at the rate of 2 tests per day. 

When the time exceeded 15 minutes the mice were helped 
out by the experimenter; a record of 15 minutes, therefore, 
indicates failure. Naturally enough the motives for escape 
were not sufficiently strong or constant to bring about the 
most rapid learning of which the dancer is capable. 
Sometimes they would remain in the wooden box washing 
themselves for several minutes before attempting to find a 



Educability : Methods of Learning 203 



TABLE 35 

Ladder Climbing Test 

Time in Minutes and Seconds 



No. OF 

Exp. 


Date 

1905 


No. 1000 


No. 2 


No. 6 


Average 
FOR All 


Daily Av. 
FOR All 


I 


Nov. 14 


15' 


15' 


15' 


— 




2 




15' 


15' 


15' 


— 


— 


3 


15 


15' 


15' 


15' 


— 


— 


4 




300" 


15' 


15' 


— 


— 


5 


16 


480" 


15' 


15' 


— 


— 


6 




180'' 


300" 


420'' 


300'' 


300" 


7 


17 


450'' 


240" 


540" 


410'' 




8 




20'' 


15'' 


18" 


18'' 


214'' 


9 


18 


90- 


180" 


135" 


135'' 




10 




135" 


105'' 


165" 


135" 


135" 


II 


19 


480'' 


240'' 


330" 


350'' 




12 




30" 


120" 


^" 


80'' 


143" 


13 


20 


360'' 


75'' 


120" 


185" 




14 




5'' 


6" 


8" 


6" 


95" 


15 


21 


105" 


450" 


120" 


192" 




16 




8" 


80" 


20" 


54'' 


123'' 


17 


22 


255'' 


300'' 


180" 


245" 




18 




\d' 


30" 


270'' 


103'' 


174" 


19 


23 


300'' 


660'' 


450" 


470" 




20 




90" 


120'' 


150'' 


120" 


295" 


21 


24 


240" 


125'' 


225" 


197" 




22 


' 


^' 


d" 


168'' 


59" 


128'' 



204 



The Dancing Mouse 
TABLE 35 — Continued 



No. OF 

Exp. 


Date 


No. TOOO 


No. 2 


No. 6 


Average 
FOR All 


Daily Av. 
FOR All 


23 


Nov. 25 


305'' 


85'' 


130'' 


173" 




24 




5" 


6" 


118" 


43" 


IO$" 


25 


26 


f 


8" 


44" 


18'' 




26 




19'' 


i'' 


176'' 


98" 


58'' 


27 


27 


150'' 


79'' 


269" 


166" 




28 




26" 


f 


31" 


20" 


93" 


29 


28 


214'' 


18" 


267" 


166" 




30 




40" 


3'' 


4" 


16" 


91" 


31 


29 


130" 


45'' 


250'' 


142" 




32 




T.1" 


3" 


25" 


13" 


77" 


33 


Dec. 2 


61" 


35" 


44" 


47" 




34 




so" 


5" 


24" 


26" 


36'' 


35 


3 


66" 


18" 


2" 


29'' 




36 




2>" 


5" 


10'' 


8" 


19" 


37 


4 


9" 


4" 


3" 


5" 




38 




10" 


5" 


6'' 


7" 


6^' 


39 


5 


5" 


3" 


5" 


4" 




40 




10'' 


4" 


3" 


6" 


5" 



way of escape. On this account I made it a rule to begin 
the time record with the appearance of active running about. 
The daily average time of escape as indicated in the table 
does not decrease regularly and rapidly. On the fourth day, 
which was the first on which all three of the dancers returned 
to the cage by way of the ladder of their own initiative in 
both tests, the average is 214 seconds. In contrast with this, 



Educability : Methods of Learning 205 

on the twentieth day the time was only 5 seconds. It is 
quite evident that the dancers had learned to climb the 
ladder. 

At the end of the twentieth day the experiment was dis- 
continued with Nos. 2 and 6, and after two weeks they were 
given memory tests, which showed that they remembered 
perfectly the ladder- climbing act, for when placed in the 
wooden box, with Nos. 4 and 5 as controls, they returned to 
the cage by way of the ladder immediately and directly. 

One of the most interesting and important features of the 
behavior of the dancer in the ladder experiment was a halt 
at a certain point on the ladder. It occurred just at the 
edge of the wooden box at the point where the ladder took a 
horizontal position, and led over into the cage. Every indi- 
vidual from the first test to the last made this halt. Although 
from the point of view of the experimenter the act was 
valueless, it may have originated as an attempt to find a 
way to escape from the uncomfortable position in which the 
animal found itself on reaching the top of the ladder. Its 
persistence after a way of escape had been found is an indica- 
tion of the nature of habit. Day after day the halt became 
shorter until finally it was little more than a pause and a 
turn of the head toward one side of the ladder. I think we 
may say that in this act we have evidence of the persistence 
of a particular resolution of physiological states which is 
neither advantageous nor disadvantageous to the organism. 
Had the act resulted in any gain, it would have become more 
marked and elaborate ; had it resulted in injury or discom- 
fort, it would have disappeared entirely. I have observed 
the same kind of behavior in the frog and in other animals. 
What the animal begins to do it persists in unless the act is 
positively harmful or conflicts with some beneficial activity. 
The only explanation of certain features of behavior is to be 



2o6 The Danci7ig Mouse 

found in the conditions of their original occurrence. They 
persist by sheer force of conservatism. They have value 
only in the light of the circumstances under which they first 
appeared. Although this is merely a fact of habit formation, 
it suggests that many of the problems v^hich have puzzled 
students of behavior for ages may be solved by a study of 
the history of activity. 

That there are marked individual differences in intelligence 
in the dancing mice is apparent from the results of the ladder- 
climbing experiment. No. looo learned to climb quickly, 
and largely by his ov^n initiative ; Nos. 2 and. 6, on the con- 
trary, learned only by reason of tuition (being put through 
the required act by the experimenter). It occurred to me 
that this experiment, since it v^as difficult for some individ- 
uals and easy for others, might be used to advantage as a 
test of imitation. If a dancer which knows how to escape 
to the cage by way of the ladder be placed in the wooden box 
with one which, despite abundant opportunity, has proved 
unable to form the habit on his own initiative, will the latter 
profit by the activity of the former and thus learn the method 
of escape ? 

On November 20, Nos. 4 and 5 were placed in the wooden 
box and left there for half an hour. As they had failed to 
escape at the end of this interval, they were taken out of the 
box by the experimenter and returned to the nest-box. 
November 21 and 22 this test of their ability to learn to 
climb the ladder was repeated with the same result. On 
November 23 they were placed in the box with the three mice 
which had previously been trained to climb the ladder. The 
latter escaped at once. Apparently the attention of Nos. 4 
and 5 was drawn to the ladder by the disappearance of their 
companions, for they approached its foot and No. 5 climbed 
up a short distance. Neither succeeded in escaping, how- 



Educability : Methods of Learning 207 

ever, and they made no further efforts that day. On the 24th, 
and daily thereafter until the 29th, these two dancers were 
placed in the box for half an hour, with negative results. 
At the end of the half hour on the 29th, Nos. 2 and 6 were 
placed in the box and permitted to go back and forth from 
one box to the other repeatedly within sight of Nos. 4 and 5. 
The latter made no attempts to follow them, although at 
times they seemed to be watching their movements as they 
ascended the ladder. 

To render the results of this test of imitation still more 
conclusive No. 5 was given further opportunity to learn from 
No. 1000. Beginning December 2, the following method of 
experimentation was employed with these two individuals. 
They were placed in the wooden box together. No. 1000 
usually climbed out almost immediately. Sometimes No. 5 
apparently saw him disappear up the ladder ; sometimes she 
paid no attention whatever either to the presence or absence 
of her companion. After he had been in the nest-box for a 
few seconds, No. 1000 was returned to the wooden box by 
the experimenter and again permitted to climb out for the 
benefit of No. 5. This mode of procedure was kept up until 
No. 1000 had made from three to ten trips. No. 5 was left 
in the box for half an hour each day. This test was repeated 
on 18 days within a period of 3 weeks. No. 5 showed no 
signs of an imitative tendency, and she did not learn to 
cHmb the ladder. 

To this evidence of a lack of an imitative tendency in the 
dancer I may here add the results of my observations in other 
experiments. In the discrimination tests and in the laby- 
rinth tests I purposely so arranged conditions, in certain 
instances, that one individual should have an opportunity to 
imitate another. In no case did this occur. Seldom indeed 
did the animals so much as follow one another with any con- 



2o8 The Dancing Mouse 

siderable degree of persistence. They did not profit by one 
another's acts. 

Excellent evidence in support of this conclusion was fur- 
nished by the behavior of the mice in the discrimination 
experiments. Some individuals learned to pull as well as 
to push the swinging wire doors of the apparatus and were 
thus enabled to pass through the doorways in either direc- 
tion; other individuals learned only to pass through in the 
direction in which the doors could be pushed open. Natu- 
rally I was interested to discover whether those which knew 
only the trick of opening the doors by pushing would learn 
to pull the doors or would be stimulated to try by seeing 
other individuals do so. At first I arranged special tests of 
imitation in the discrimination box ; later I observed the in- 
fluence of the behavior of one mouse upon that of its com- 
panion in connection with visual discrimination experiments. 
This was made possible by the fact that usually a pair of in- 
dividuals was placed in the discrimination box and the tests 
given alternately to the male and to the female. Both indi- 
viduals had the freedom of the nest-box and each frequently 
saw the other pass through the doorway between the nest- 
box, A^ and the entrance chamber, B (Figure 14), either from 
v4 to 5 by pushing the swing door or from B \.o A by pulling 
the door. 

Although abundant opportunity for imitation in connection 
with the opening of the doors in the discrimination box was 
given to twenty-five individuals, I obtained no evidence of 
ability to learn by imitation. The dancers did not watch the 
acts which were performed by their companions, and in most 
instances they did not attempt to follow a mate from nest- 
box to entrance chamber. 

These problem tests, simple as they are, have revealed two 
important facts concerning the educability of the dancer. 



Educability : Methods of Learning 209 

First, that it does not learn by imitation to any considerable 
extent, and, second, that it is aided by being put through 
an act. Our general conclusion from the results of the ex- 
periments which have been described in this chapter, if any 
general conclusion is to be drawn thus prematurely, must be 
that the dancing mouse in its methods of learning differs 
markedly from other mice and from rats. 



CHAPTER XIII 
Habit Formation: The Labyrinth Habit 

The problem method, of which the ladder and door-opening 
tests of the preceding chapter are examples, has yielded inter- 
esting results concerning the individual initiative, ingenuity, 
motor ability, and ways of learning of the dancer ; but it has 
not furnished us with accurate measurements of the rapidity 
of learning or of the permanency of the effects of training. 
In this chapter I shall therefore present the results of laby^ 
rinth experiments which were planned as means of measuring 
the intelligence of the dancer. 

The four labyrinths which have been used in the investi- 
gation may be designated SiS A, B, C, and D. They differ 
from one another in the character of their errors, as well as 
in the number of wrong choices of a path which the animal 
might make on its way from entrance to exit. In the use 
of the labyrinth method, as in the case of the discrimination 
method of earlier chapters, the steps by which a satisfactory 
form of labyrinth for testing the dancer was discovered are 
quite as interesting and important for those who have an 
intelligent appreciation of the problems and methods of ani- 
mal psychology as are the particular results which were ob- 
tained. For this reason, I shall describe the various forms 
of labyrinth in the order in which they were used, whether 
they proved satisfactory or not. At the outset of this part of 
my investigation, it was my purpose to compare directly 
the capacity for habit formation in the dancer with that of 

2IO 



Habit Formation : The Labyrinth Habit 211 



the common mouse. This proved impracticable because the 
same labyrinth is not suited to the motor tendencies of both 
kinds of mice. 

The first of the four labyrinths, A, appears in ground plan 
in Figure 25. It was constructed of wood, as were the other 
labyrinths also, 
and measured 
60 cm, in length 
and width, and 
10 cm. in depth. 
The outside 
alleys were 5 
cm, wide. In 
the figure, / 
marks the start- 
ing point or en- 
trance to the 
maze, and O 
the exit through 
which the 
mouse was per- 
mitted to pass into its nest-box. Any turn in the wrong direc- 
tion which the animal made in its progress from entrance to 
exit was recorded as an error. The four errors, exclusive of the 
mistake of turning back, which were possible in this labyrinth, 
are indicated in the figure by the numerals i, 2, 3, and 4. 
By retracing its steps a mouse might repeat any one or all of 
these errors, and add to them the error of turning back. 

In the experiments a mouse was permitted to enter the 
maze from a small box which had been placed by the experi- 
menter at 7, and an accurate record was kept of the number 
of errors which it made in finding its way from entrance to 
exit, and of the time occupied. Each of five dancers was given 




Figure 25. — Labyrinth A. /.entrance; O, exit; i, 2, 
3, 4, blind alleys. 



212 The Dancing Mouse 

31 tests in this labyrinth. The number of tests per day 
varied, as is indicated in Table 36, from i to 4. The results 
of the tests, so far as errors and times are in question, appear 
in the table. T at the head of a column is an abbreviation 
for time, E for errors. 

The dancers did not learn to escape from this labyrinth 
easily and quickly. In fact, the average time of the thirty- 
first test (198'') is considerably longer than that of the first 
(130"). The number of errors decreased, it is true, but even 
for the last test it was 6.6 as compared with only a little more 
than twice that number for the first test. The last column 
of the table furnishes convincing proof of the truth of the 
statement that the animals did not acquire a perfect labyrinth- 
A habit. Was this due to inability to learn so complex a 
path, or to the fact that the method is not adapted to their 
nature? Observation of the behavior of the mice in the 
experiments enables me to say with certainty that there was 
no motive for escape sufficiently strong to establish a habit 
of following the direct path. Often, especially after a few 
experiences in the maze, a dancer would wander back and 
forth in the alleys and central courts, dancing much of the 
time and apparently exploring its surroundings instead of 
persistently trying to escape. This behavior, and the time 
and error results of the accompanying table, lead me to con- 
clude that the labyrinth method, as it has been employed in 
the study of the intelligence of several other mammals, is not 
a satisfactory test of the ability of the dancer to profit by 
experience. That the fault is not in the labyrinth itself is 
proved by the results which I obtained with common mice. 

On the basis of two tests per day, two common mice, a 
white one and a gray one, quickly learned to escape from 
labyrinth A by the shortest path. The time of escape for 
the gray individual (Table 37) decreased from 180" in the 



Habit Formation : The Labyrinth Habit 213 



TABLE 36 
Results of Labyrinth-A Tests with Dancers 







No. I 


DOO 


No. 


2 


No. 


6 


No. 


4 


No. 


5 


AvEt 

FOR 


AGE 

All 


Test 


Date 
1905 




























T 


E 


T 


E 


T 


E 


T 


E 


T 


E 


T 


E 


I 


Nov. 23 


130" 


14 


100" 


8 


170" 


13 


60" 


6 


190" 


26 


130" 


13-4 


2 


2i 


140 


19 


' 78 


7 


60 


8 


149 


6 


211 


25 


128 


13.0 


3 


25 


392 


31 


87 


I 


98 


5 


185 


13 


120 


9 


176 


11.8 


4 


26 


448 


38 


38 


3 


47 


2 


50 


3 


121 


12 


141 


II-3 


5 


27 


142 


8 


21 


2 


27 


3 


27 


2 


• 17 


I 


47 


3-2 


6 


28 


45 


2 


61 


7 


63 


5 


102 


8 


2>2> 


4 


61 


5-2 


7 


29 


303 


17 


64 


7 


36 


3 


42 


2 


57 


4 


100 


6.6 


8 


30 


222 


15 


26 


2 


37 


5 


42 


3 


7 





67 


5-0 


9 


Dec. I 


i8s 


9 


36 


5 


48 


3 


63 


3 


94 


8 


85 


5-6 


10 


2 


52 


2 


71 


4 


19 





196 


5 


95 


11 


87 


4.4 


II 


3 


180 


8 


32 


2 


107 


4 


52 


3 


38 


4 


82 


4.2 


12 


4 


310 


10 


^2,Z 


II 


65 


3 


242 


6 


125 


6 


175 


7.2 


13 


4 


153 


9 


335 


55 


130 


10 


195 


15 


154 


18 


193 


21.4 


14 


5 


330 


7 


69 


2 


42 


2 


201 


6 


130 


10 


154 


5-4 


15 


5 


287 


7 


34 


4 


61 


4 


136 


7 


25 


2 


109 


4.8 


16 


S 


455 


15 


65 


4 


25 





no 


8 


160 


15 


183 


8.4 


17 


6 


120 


15 


280 


9 


2,1 





168 


4 


39 


2 


128 


6.0 


18 


6 


120 


4 


164 


10 


81 


4 


lOI 


5 


85 


4 


no 


5-4 


19 


6 


132 


12 


78 


7 


no 


6 


40 


2 


151 


12 


102 


7.8 


20 


7 


258 


10 


223 


16 


33 


I 


92 


5 


37 


I 


129 


6.6 


21 


7 


no 


7 


23 


3 


44 


4 


20 


4 


305 


23 


100 


8.2 


22 


7 


100 


4 


60 


8 


167 


15 


44 


7 


58 


4 


86 


7.6 


23 


8 


43 


I 


179 


7 


356 


6 


34 


3 


65 


3 


135 


4.0 


24 


8 


92 


5 


56 


5 


42 


3 


17 


I 


23 


I 


46 


3-0 


25 


9 


85 


5 


114 


3 


62 


3 


129 


8 


31 





84 


3-8 


26 


9 


30 


2 


36 


4 


109 


15 


12 


^ 


34 


2 


44 


4.8 


27 


9 


69 


5 


40 


4 


85 


6 


36 


3 


16 


• I 


49 


3-8 


28 


10 


160 


7 


80 


3 


28 





142 


5 


35 


2 


89 


3-4 


29 


10 


155 


5 


266 


8 


91 


5 


27 





37 


2 


"5 


4.0 


30 


10 


29 


I 


25 


2 


124 


14 


83 


6 


III 


12 


74 


7.0 


31 


10 


465 


6 


208 


8 


95 


3 


65 


3 


159 


13 


198 


6.6 



first test to 21" in the tenth, and the number of errors from 
6 to I. Similarly in the case of the white individual, the time 
decreased from 122'' to 8'', and the errors from 5 to i. A 



214 



The Dancing Mouse 



fraction of the number of tests to which the dancer had been 
subjected sufficed to estabHsh a habit of escape in the com- 
mon mouse. It is evident, therefore, that the dancer differs 
radically from the common mouse in its behavior in a maze; 
and it is also clear that the labyrinth method, if it is to be 
used to advantage, must be adapted to the motor tendencies 
of the animal which is to be tested. 



TABLE 37 • 
Results of Labyrinth-A Tests with Common Mice 





Test 


Gr"ey Mouse 


White Mouse 












T 


e 


T 


e 


I 


i8o" 


6 


122" 


5 


2 


26 


2 


8o 


6 


3 


37 


I 


56 


4 


4 


i8 


O 


27 


I 


5 


68 


2 


ZZ 


2 


6 


lO 


I 


19 




7 


II 


I 


17 




8 


13 


I 


17 




9 


lO 


O 


8 




lO 


21 


I, 


8 





The behavior of the dancer made obvious two defects in 
labyrinth A. Its passages are so large that the mouse is 
constantly tempted to dance, and it lacks the basis for a 
strong and constant motive of escape by the direct path. To 
obviate these shortcomings labyrinth B was constructed, as 
is shown in Figures 23 and 24, with very narrow passages, 
and a floor which was covered with the wires of an interrupted 
electric circuit so that errors might be punished. The length 



I 



k 



Habit Formation : The Labyrinth Habit 215 

of this labyrinth was 52 cm. and the passages were 2.5 cm. 
wide and 10 cm. deep. Dancing in these narrow alleys was 
practically impossible, for the mice could barely turn around 
in them. In the case of all except the common mice and 
two dancers, a depth of 10 cm. was sufficient to keep the 
animals in the maze without the use of a cover. 

As an account of the behavior of the dancer in labyrinth 
B has already been given in Chapter XI, I may now state 
the general results of the experiments. In all, thirty indi- 
viduals were trained in this labyrinth. Each individual 
was given tests at the rate of one per minute until it had suc- 
ceeded in following the correct path five times in succession. 
The weak electric shock, which was given as a punishment for 
mistakes, provided an activity-impelling motive for escape to 
the nest-box. 

An idea of the extreme individual difference in the rapidity 
with which the labyrinth- B path was learned by these dancers 
may be obtained by an examination of Table 38, from which 
it appears that the smallest number of training tests neces- 
sary for a successful or errorless trip through the maze was 
one and the largest number fourteen. It is to be remembered 
that each mouse was given an opportunity to pass through 
the labyrinth once without punishment for errors, and thus 
to discover, before the training tests were begun, that a way 
of escape existed. This first test we may designate as the 
preliminary trial. Table 38 further indicates that the females 
acquired the labyrinth habit more quickly than did the males. 

A graphic representation of certain of the important features 
of the process of formation of the labyrinth-B habit is fur- 
nished by Figure 26 in which the solid line is the curve of 
learning for the ten males of Table 38, and the broken Hne 
for the ten females. These two curves were plotted from the 
number of errors made in the preliminary trial (P in the figure) 



210 



The Dancing Mouse 



TABLE 38 
Results of Labyrinth-B Experiments, with Twenty Dancers 



Males 


Females 


No. OF 

Mouse 


No. OF First 

Correct 

Test 


No. OF Last of 

Five Correct 

Tests 


No. OF 

Mouse 


No. OF First 

Correct 

Test 


No. of Last of 

Five Correct 

Tests 


76 


8 


14 


75 


4 


15 


78 


5 


20 


77 


7 


II 


86 


13 


22 


87 


12 


22 


58 


2 


14 


49 


I 


5 


50 


6 


23 


57 


3 


20 


60 


13 


37 


59 


14 


28 


410 


6 


20 


415 


4 


13 


220 


4 


8 


225 


6 


18 


212 


3 


7 


211 


6 


10 


• 214 


10 


28 


213 


5 


14 


Av. 


7.0 


19-3 


Av. 


6.2 


15-6 



and in each of the subsequent tests up to the sixteenth. In 
the case of both the males and the females, for example, the 
average number of errors in the preliminary trial was 11.3, as 
is indicated by the fact that the curves start at a point whose 
value is given in the left margin as 11. 3. In the second 
training test the number of errors fell to 3.3 for the males and 
2.7 for the females. The number of the test is to be found 
on the base line ; the number of errors in the left margin. If 
these two curves of learning were carried to their comple- 
tion, that for the males would end with the thirty-seventh 
test, and that for the females with the twenty-eighth. 
' Time records are not reported for these and subsequent 
labyrinth tests because they proved to be almost valueless 



Habit Formation: The Labyri7ith Habit 217 

as measures of the rapidity of habit formation. At any point 
in its progress through a labyrinth, the dancer may suddenly 
stop to wash its face, look about or otherwise examine its 
surroundings ; if a shock be given to hurry it along it may 



11 


9 
8 
7 
6 
5 
4 
3 
2 
I 
































\ 






























1 






























\ 






























\ 






























\ 
\ 






























\ 
1 
\ 
































\ \ 
\ \ 






























\ \ 
\ ) 
\ 


•v 


/ 


























\ 


N 


/ 


\ 


























'n 


-^.^ 


\ 




^^ 




> 


V 






>^ 
















■*■«• 


— 


'-' 


>< 


> 


^^ 


..X 


rrr:: 


<i 


V 


:t> 


:::: 



P 1 2 3 4 6 6 7 8 9 10 U 12 13 14 15 

Figure 26. — Curves of habit formation, plotted from the data of labyrinth-B tests 
with ten males and ten females. The figures in the left margin indicate the number 
~ii errors; those below the base line the number of the test. P designates the prelimi- 
nary test. Males ; Females . 

be surprised into an error. It is my experience, ^nd this is 
true of other animals as well as of the dancing mouse, that a 
long trip, as measured in time units, does not necessarily 
indicate the lack of ability to follow the labyrinth path 
correctly and rapidly. Hence, whenever it is possible (and 
the experimenter can always plan his tests so that it shall be 
possible), the number of errors should be given first impor- 



2i8 The Dancing Mouse 

tance and the time of the test second place. I have presented 
in Table 38 the number of the first correct test, and the 
number of the last of five successive correct tests. . Space 
cannot be spared for records of the errors made in the 
several tests by each individual. 

In general, labyrinth B proved very satisfactory as a means 
of testing the ability of the dancer to learn a simple path. 
The narrow passages effectively prevented dancing, and the 
introduction of the electric shock as a punishment for mistakes 
developed a motive for escape which was uniform, constant, 
and so strong that the animals clearly did their best to escape 
from the labyrinth quickly and without errors. This maze 
was so simple that it did not tend to discourage them as did 
the one which is next to be described. It must be admitted, 
however, that, though labyrinth B is perfectly satisfactory 
as a test of the dancer's ability to learn to follow a simple path, 
it is not an ideal means of measuring the rapidity of habit 
formation. This is due to the fact that the preliminary trial 
and the first training test play extremely different roles in 
the case of different individuals. A dancer which happens to 
follow the correct path from entrance to exit in the prelim- 
inary trial may continue to do so, with only an occasional 
error, during several of the early training tests, and it may 
therefore fail for a considerable time to discover that there are 
errors which should be avoided. The learning process is 
delayed by its accidental success. On the other hand, an 
individual which happens to make many mistakes to begin 
with immediately attempts to avoid the points in the maze 
at which it receives the electric shock. I was led to conclude, 
as a result of the labyrinth-B experiments, that the path was 
too easy, and that a more complex labyrinth would, in all 
probability, furnish a more satisfactory means of measuring 
the rapidity of habit formation. 



Habit Formation: The Labyrinth Habit 219 

On the basis of the supposition that a maze whose path 
was so complex that the animal would not be likely to follow 
it correctly in the early trials would be more to the purpose 

Title of investigation..... ,...:LabyxintJl C. ;.,„.,, 

Experimented on "P,.».~.. ...„...,...i.. 

Harvard Psych. Lab., February 26, , 1907. 




Test 1 
Errors 12 




Test 5 
Errors 5 



If 



fS 



Test 10 
Errors 1 



G 



5/ 



/[ 



r- 



Test 11 
Errors 



Figure 27. — A record sheet, showing the plan of labyrinth C (as made on the 
sheet by means of a rubber stamp) on which the experimenter recorded the path 
followed by the mouse. This sample sheet presents the path records for the 
first, fifth, tenth, and eleventh tests of No. 2 in labyrinth C. i, 2, 3, 4, 5 desig- 
nate the several errors of the labyrinth. 



^20 The Dancing Mouse 

than either A or B, labyrinth C was devised. As is shown 
in the plan of this maze, Figure 27, five mistakes in choice 
of path were possible on the forward trip. These errors, as 
a rule, were more difficult for the dancers to avoid than those 
of labyrinths A and B. Those which are designated by the 
numerals 2, 3, and 4 were especially difficult. Error 4 
was much more troublesome for left whirlers than for right 
whirlers because, after turning around abruptly at the entrance 
to the blind alley, the former type of dancer almost always 
followed the side wall of the maze so far that it missed the 
correct path. Undoubtedly the various errors are not of the 
same value for different individuals ; but it would be extremely 
difficult, if not impossible, to devise a maze which should 
be equally difficult for several normal individuals. 

In order that records of the path followed by a mouse in 
test after test might be kept with ease and accuracy by the 
experimenter, the plan of this labyrinth, and also that of 
labyrinth D, were cast in rubber. The outlines of labyrinths 
C and D which appear in Figures 27 and 28 respectively were 
made with the rubber stamps which were thus obtained. 
Figure 27 is the reproduction of a record sheet which presents 
the results of the first, the fifth, the tenth, and the eleventh 
tests of No. 2 in labyrinth C. The path followed by this 
individual in the first test was far too complex to be traced 
accurately on the record sheet. The record therefore repre- 
sents merely the number of errors which was made in each 
region of the maze. For the fifth test, and again for the tenth 
and the eleventh, the path was recorded accurately. This 
simple device for making record blanks which can readily 
be filled in at the time of the experiment should recom- 
mend itself to all students of animal behavior. 

In labyrinth C ten pairs of dancers were given continuous 
training tests at the rate of one test per minute until they were 



Habit Formation: The Labyrinth Habit 221 

able to follow the direct path correctly. Because of the diffi- 
culty in learning this maze perfectly, it was not demanded of 
the mice that they should follow the path correctly several 
times in succession, but instead the training was terminated 
after the first successful trip. 

The results of the experiments with this labyrinth as they 
are presented in Table 39 indicate that its path is considerably 
more difficult for the dancer to learn than that of labyrinth 
B, that the females learn more quickly than the males, and 
finally, that individual differences are just as marked as they 
were in the case of the simpler forms of labyrinth. It there- 
fore appears that increasing the complexity of a labyrinth 
does not, as I had supposed it might, diminish the variability 
of the results. Certain of the individual differences which 

TABLE 39 
Results of Labyrinth-C Experiments, with Twenty Dancers 



Males 


Females 


No. OF 
Mouse 


No. OF First 
Correct Test 


No. OF 
Mouse 


No. of First 
Correct Test 


2 


II 


29 


15 


30 


ZZ 


49 


34 


50 


49 


57 


15 


52 


22 


59 


15 


58 


16 


215 


10 


60 


17 


415 


10 


76 


3 


75 


8 


78 


6 


77 


II 


86 


5 


87 


9 


88 


25 


85 


II 


Av. 


18.7 


Av. 


13.8 



I 



13 




o 

10 


12 




9 




8 




7 


5 




6 


4 




3 


1 




2 



222 The Dancing Mouse 

appear in Table 39 are due, however, to the fact that in some 
cases training in labyrinth B had preceded training in laby- 
rinth C, whereas in the other cases C was the first labyrinth 
in which the animals were tested. But even this does not 
serve to account for the wide divergence of the results given 

by No. 2 and No. 50, for the 
latter had been trained in B 
previous to his training in C, 
and the former had not been so 
trained. Yet, despite the advan- 
tage which previous labyrinth 

Figure .8. -Plan of Labyrinth experience gave No. 50, he did 

D, as reproduced from a print made not learn the path of C as WCll 

with a rubber stamp /. entrance; -^ ^^ ^^^^^ ^^ ^^ ^ ^j^ j^ 

O, exit; numerals i to 13, errors. -^ 

eleven. The facts concern- 
ing the value of training in one form of labyrinth for the learn- 
ing of another, as they were revealed by these experiments, 
may more fittingly be discussed in a later chapter in connec- 
tion with the facts of memory and re-learning. 

Labyrinth C is a type of maze which might properly be 
described as irregular, since the several possible errors are 
extremely different in nature. In view of the results which 
this labyrinth yielded, it seemed important that the dancer 
be tested in a perfectly regular maze of the labyrinth-D type. 
The plan which I designed as a regular labyrinth has been 
reproduced, from a rubber stamp print, in Figure 28. As 
is true also of the mazes previously described, it provides 
four kinds of possible mistakes : namely, by turning to the 
left (errors i, 5, 9, and 13), by turning to the right (errors 
3, 7, and 11), by moving straight ahead (errors 2, 4, 6, 8, 10, 
and 12), and by turning back and retracing the path just 
followed. . The formula for the correct path of D is simple 
in the extreme, in spite of the large number of mistakes which 



Habit Formation : The Labyrinth Habit 223 

are possible, for it is merely ''a turn to the right at the en- 
trance, to the left at the first doorway, and thereafter alter- 
nately to the right and to the left until the exit is reached." 
This concise description would enable a man to find his 
way out of such a maze with ease. Labyrinth D had been 
constructed with an exit at 10 so that it might be used as a 
nine-error maze if the experimenter saw fit, -or as a thirteen- 
error maze by the closing of the opening at 10. In the ex- 
periments which are now to be described only the latter form 
was used. 

Can the dancer learn a regular labyrinth path more quickly 
than an irregular one ? Again, I may give only a brief state- 
ment of results. Each of the twenty dancers, of Table 
40, which were trained in labyrinth D had previously been 
given opportunity to learn the path of C, and most of them 
had been trained also in labyrinth B. All of them learned 
this regular path with surprising rapidity. The numerical 
results of the tests with labyrinths B, C, and D, as well as 
the behavior of the mice in these several mazes, prove con- 
clusively that the nature of the errors is far more important 
than their number. Labyrinth D with its thirteen chances 
of error on the forward trip was not nearly as difficult for 
the dancer to learn to escape from as labyrinth C with its 
five errors. That the facility with which the twenty individ- 
uals whose records are given in Table 40 learned the path 
of D was not due to their previous labyrinth experience 
rather than to the regularity of the maze is proved by the 
results which I obtained by testing in D individuals which 
were new to labyrinth experiments. Even in this case, the 
number of tests necessary for a successful trip was seldom 
greater than ten. If further evidence of the ease with which 
a regular labyrinth path may be followed by the dancer 
were desired, it might be obtained by observation of the 



224 



The Dancing Mouse 



TABLE 40 
Results of Labyrinth-D Experiments, with Twenty Dancers 



Males 


Females 


No. OF 
Mouse 


No. OF First 

Correct 

Test 


No. of Last of 

Two Correct 

Tests 


No. of 
Mouse 


No. OF Fif'ST 

Correct 
Test 


No. OF Last of 

Two Correct 

Tests 


2 


3 


7 


29 


10 


II 


58 


7 


10 


49 


7 


8 


30 


9 


10 


57 


3 


6 


60 


10 


14 


215 


6 


10 


402 


10 


II 


415 


7 


8 


76 


4 


7 


75 


4 


13 


78 


4 


5 


77 


II 


12 


86 


3 


9 


87 


4 


9 


88 


4 


8 


85 


3 


4 


90 


7 


8 


83 


4 


7 


Av. 


6.1 


8.9 


Av. 


5-9 


8.8 



behavior of an individual in labyrinths C and D. In the 
former, even after it has learned the path perfectly, the mouse 
hesitates at the doorways from time to time as if uncertain 
whether to turn to one side or go forward ; in the latter there 
is seldom any hesitation at the turning points. The irregular 
labyrinth is followed carefully, as by choice of the path from 
point to point ; the regular labyrinth is followed in machine 
fashion, — once started, the animal dashes through it. 

From the results of these labyrinth experiments with 
dancers I am led to conclude that a standard maze for test- 
ing the modifiability of behavior of different kinds of animals 
should be constructed in conformity with the following sug- 
gestions. Errors by turning to the right, to the left, and by 
moving forward should occur with equal frequency, and in 



Habit Formation: The Labyrinth Habit 225 

such order that no particular kind of error occurs repeatedly 
in succession. If we should designate these three types of 
mistake by the letters r, /, and 5 respectively, the error series 
of labyrinth C would read l-l-r-s-l. It therefore violates 
the rule of construction which I have just formulated. In 
the case of labyrinth D the series would read l-s-r-s-l-s-r-s-l-S' 
r-s-l. This also fails to conform with the requirement, for 
there are three errors of the first type, four of the second, and 
six of the third. Again, in a standard maze, the blind alleys 
should all be of the same length, and care should be taken to 
provide a sufficiently strong and uniform motive for escape. 
In the case of one animal the desire to escape from confine- 
ment may prove a satisfactory motive ; in the case of another, 
the desire for food may conveniently supplement the dislike of 
confinement ; and in still other cases it may appear that some 
form of punishment for errors is the only satisfactory basis 
of a motive for escape. Readers of this account of the be- 
havior of the dancing mouse must not infer from my experi- 
mental results that the electric shock as a means of forcing 
discrimination will prove satisfactory in work with other 
animals or even with all other mammals. As a matter of 
fact it has already been proved by Doctor G. van T. Hamil- 
ton that the use of an electric shock may so intimidate a 
dog that experimentation is rendered difficult and of little 
value. And finally, in connection with this discussion of 
a standard labyrinth, I wish to emphasize the importance of 
so recording the results of experiments that they may be in- 
terpreted in terms of an animal's tendency to turn to the right 
or to the left. My work with the dancer has clearly shown 
that the avoidance of a particular error may be extremely 
difficult for left whirlers and very easy for right whirlers.' 

I hope I have succeeded in making clear by the foregoing 
account of my experiments that the labyrinth method is more 

Q 



2 26 The Dancing Mouse 

satisfactory in general than the problem method as a means 
of measuring the rapidity of habit formation in the dancer, 
and I hope that I have made equally clear the fact that it 
is very valuable as a means of discovering the roles of 
the various senses in the acquirement of a habit (Chapter 
XI). From my own experience in the use of the labyrinth 
with the dancer and with other animals, I am forced to con- 
clude that its chief value lies in the fact that it enables the 
experimenter so to control the factors of a complex situation 
that he may readily determine the importance of a given 
kind of sense data for the formation or the execution of a 
particular habit. As a means of measuring the intelligence ; i, 
of an animal, of determining the facility with which it isj 
capable of adjusting itself to new environmental conditions,' 
and of measuring the permanency of modifications which 
are wrought in its behavior by experimental conditions, I 
value the labyrinth method much less highly now than I did 
previous to my study of the dancer. It is necessarily too com- \ 
plex for the convenient and reasonably certain interpretation 
of results. Precisely what is meant by this statement will 
be evident in the light of the results of the application of the 
discrimination method to the dancer, which are to be pre- 
sented in the next chapter. The labyrinth method is an 
admirable means of getting certain kinds of qualitative re- 
sults ; it is almost ideal as a revealer of the role of the senses, 
and it may be used to advantage in certain instances for the 
quantitative study of habit formation and memory. Never- 
theless, I think it may safely be said that the problem method 
and the discrimination method are likely to do more to ad- 
vance our knowledge of animal behavior than the labyrinth 
method. 



CHAPTER XIV 
Habit Formation: The Discrimination Method 

Discrimination is demanded of an animal in almost all 
forms of the problem and labyrinth methods, as well as in 
what I have chosen to call the discrimination method. In 
the latter, however, discrimination as the basis of a correct 
choice of an electric-box is so obviously important that it 
has seemed appropriate to distinguish this particular method 
of measuring the intelligence of the dancer from the others 
which have been used, by naming it the discrimination method. 

It has been shown that neither the problem nor the labyrinth 
method proves wholly satisfactory as a means of measuring 
the rapidity of learning, or the duration of the effects of train- 
ing, in the case of the dancer. The former type of test serves 
to reveal to the experimenter the general nature of the ani- 
mal's capacity for profiting by experience; the latter serves 
equally well to indicate the parts which various receptors 
(some of which are sense organs) play in the formation and 
execution of habits. But neither of them is sufficiently simple, 
easy of control, uniform as to conditions which constitute 
bases for activity, and productive of interpretable quanti- 
tative results to render it satisfactory. The problem method 
is distinctly a qualitative method, and, in the case of the danc- 
ing mouse, my experiments have proved that the labyrinth 
method also yields results which are more valuable quali- 
tatively than quantitatively. I had anticipated that various 
forms of the labyrinth method would enable me to measure 

227 



2 28 The Dancmg Mouse 

the modifiability of behavior in the dancer with great accuracy, / 
but, as will now be made apparent, the discrimination method/ 
proved to be a far more accurate method for this purpose. 

Once more I should emphasize the fact that my statements 
concerning the value of methods apply especially to the 
dancing mouse. Certain of the tests which have proved to 
be almost ideal in my study of this, peculiar little rodent would 
be useless in the study of many other mammals. An ex- 
perimenter must work out his methods step by step in the 
light of the daily results of patient and intelhgent observa- 
tion of the motor capacity, habits, instincts, temperament, 
imitative tendency, intelligence, hardihood, and life-span of 
the animal which he is studying. The fact that punishment 
has proved to be more satisfactory than reward in experiments 
with the dancer does not justify the inference that it is more 
'satisfactory in the case of the rat, cat, dog, or monkey. Meth- 
ods which yielded me only qualitative results, if applied to 
other mammals might give accurate quantitative results; 
and, on the other hand, the discrimination method, which has 
proved invaluable for my quantitative work, might yield only 
qualitative results when applied to another kind of animal. 

The form of the discrimination method whose results are 
to be presented in this, chapter has already been described 
as white-black discrimination. In the discrimination box 
(Figures 14 and 15, p. 92) the two electric- boxes which were 
otherwise exactly ahke in appearance were rendered dis- 
criminable for the mouse by the presence of white cardboards 
in one and black cardboards in the other. In order to escape 
from the narrow space before the entrances to the two elec- 
tric-boxes, the dancer was required to enter the white box. 
If it entered the black box a weak electric shock was experi- 
enced. After two series of ten tests each, during which the 
animal was permitted to choose either the white or the black 



Habit Formation : Discriminatioii Method 229 

box without shock or hindrance, the training was begun. 
These two prehminary series serve to indicate the natural 
preference of the animal for white or black previous to the 
training. An individual which very strongly preferred the 
white might enter, from the first, the box thus distinguished, 
whereas another individual whose preference was for the 
black might persistently enter the black box in spite of the 
disagreeable shocks. First of all, therefore, the preliminary 
tests furnish a basis for the evaluation of the results of the 
subsequent training tests. On the day succeeding the last 
series of preliminary tests, and daily thereafter until the ani- 
mal had acquired a perfect habit of choosing the white box, 
a series of training tests was given. These experiments 
were usually made in the morning between nine and twelve 
o'clock, in a room with south-east windows. The entrances 
to the electric- boxes faced the windows, consequently the 
mouse did not have to look toward the light when it was 
trying to discriminate white from black. All the conditions 
of the experiment, including the strength of the current for 
the shock, were kept as constant as possible. 

Choice by position was efifectively prevented, as a rule, 
by shifting the cardboards so that now the left now the right 
box was white. The order of these shifts for the white- 
black series whose results are quantitatively valuable appear 
in Table 12 (p. iii). That ths order of these changes in 
position may be criticised in the light of the results which 
the tests gave, I propose to show hereafter in connection with 
certain other facts. The significant point is that the defects 
which are indicated by the averages of thousands of tests 
could not have been predicted with certainty even by the 
most experienced investigator in this field. 

In Table 41 are to be found the average number of errors 
in each series of ten white-black discrimination tests for five 



230 



The Dancing Mouse 



males and for five females which were trained by being given 
ten tests per day, and similarly for the same number of in- 
dividuals of each sex, trained by being given twenty tests 
per day. Since the results for these two conditions of training 
are very similar, the averages for the twenty individuals are 
presented in the last column of the table. For the present 
we may neglect the interesting individual, sex, and age differ- 



TABLE 41 

WmxE Black Discrimination Tests. Number of Errors in 
THE Various Series 





Males 


Females 


1 
Averages 
















Series 


Averages 

FOR 5, 10 

Tests pep 

Day 


Averages 

FOR 5, 20 

Tests per 

Day 


General 

Averages 

for 10 


Averages 

FOR =;, 10 

Tests per 

Day 


Averages 

FOR 5, 20 

Tests per 

Day 


General 

Averages 

FOR 10 


FOR ALL (20) 

Males and 
Females 


A 


5.8 


6.0 


5-9 


5-8 


5-8 


5-8 


5.85 


B 


5-6 


6.2 


5-9 


5-8 


5-6 


5-7 


5-8 


I 


5-0 


5-0 


5-0 


5-6 


4.6 


5-1 


5-05 


2 


2.6 


4.6 


3.6 


4.4 


5-0 


4-7 


4-i.S 


3 


3-0 


3-4 


z--^ 


3.4 


3-4 


3.4 


Z-l 


4 


2.6 


3.8 


3-2 


2.4 


2.2 


2.3 


2-75 


5 


2.4 


2.0 


2.2 


2.6 


1.8 


2.2 


2.2 


6 


1.6 


1.6 


1.6 


1.0 


2.2 


1.6 


1.6 


7 


I.O 


1.4 


1.2 


2.0 


0.4 


1.2 


1.2 


8 


0.2 


0.6 


•4 


1.4 


1.6 


1-5 


•95 


9 


0.2 


1.0 


.6 


0.6 


0.8 


•7 


•65 


10 





.8 


•4 


1.0 


0.8 


•9 


•65 


II 





.8 


•4 


0.8 





.4 


.40 


12 





.6 


•3 


0.4 





.2 


•25 


13 























14 






















15 























Habit Formation : Discrimination Method 231 

ences which these experiments revealed and examine the 
significant features of the general averages, and of the white- 
black discrimination curve (Figure 29). 

The preference series, A and B, reveal a constant tendency 
to choose the black box, whose strength as compared with 



6 :::z:i- ^ 

5 _^i^_ ^ 

4 S— 

3 ^X. : 

1 :=s»^- 



A 6 \ Z 3 4 (S, 6. 7 d> » 10, U ^Z. ^13 14 

Figure 29. — Error curve plotted from the data given by twenty dancers in white- 
black discrimination tests. The figures in the left margin indicate the number of 
errors ; those below the base line, the number of the series. A and B designate the 
preference series. 

the tendency to choose the white box is as 5.8 is to 4.2. In 
other words, the dancer on the average chooses the black 
box almost six times in ten. The first series of training 
tests reduced this preference for black to zero, and succeeding 
series brought about a rapid and fairly regular decrease in 
the number of errors, until, in the thirteenth series, the white 
was chosen every time. / Since I arbitrarily define a perfect 
habit of discrimination as the ability to choose the right box 
in three successive series of ten tests each, the tests ended! 
with the fifteenth series. 

The discrimination curve. Figure 29, is a graphic represen- 
tation of the general averages of Table 41. It is an error 
curve, therefore. Starting at 5.85 for the first preliminary 



232 The Dancing Mouse 

series, it descends to 5.8 for the second series, and thence 
abruptly to 5.05 for the first training series. This series of 
ten tests therefore serv^ed to reduce the black preference very 
considerably. The curve continues to descend constantly 
until the tenth series, for which the number of errors was the 
same as for the preceding series, .65. This irregularity in 
the curve, indicative, as it would appear, of a sudden cessation 
in the learning process, demands an explanation. My first 
thought was that an error in computation on my part might 
account for the shape of the curve. The error did not exist, 
but in my search for it I discovered what I now believe to 
be the cause of the interruption in the fall of the error curve. 
In all of the training series up to the tenth the white card- 
board had been on the right and the left alternately or on 
one side two or three times in succession, whereas in the tenth 
series, as may be seen by referring to Table 12 (p. in), it was 
on the left for the first four tests, then on the right four times, 
and, finally, on the left for the ninth test and on the right for 
the tenth. This series was therefore a decidedly more severe 
test of the animal's ability to discriminate white from black 
and to choose the white box without error than were any that 
had preceded it. If my interpretation of the results is correct, 
it was so much more severe than the ninth series that the 
process of habit formation was obscured. It would not be 
fair to say that the mouse temporarily ceased to profit by 
its experience; instead it profited even more than usually, 
in all probabiHty, but the unavoidably abrupt increase in 
the difficultness of the tests was just sufficient to hide the 
improvement. 

As I have suggested, the plan of experimentation may 
be criticised adversely in the light of this irregularity in the 
error curve. Had the conditions been perfectly satisfactory 
the curve would not have taken this form. I admit this, but 



Habit Formation : Discrimi^iation Method 233 

at the same time I am glad that I chose that series of shifts 
in the position of the cardboards which, as it happens, served 
to exhibit an important aspect of quantitative measures of 
the modifiabihty of behavior that otherwise would not have 
been revealed. Our mistakes in method often teach us more 
than our successes. I have taken pains, therefore, to describe 



e ;— 

5 ^_ 

4 \_ 

3 bik,;-- 

2 — ^s^5- 

1 '■ =^-<=r 



A B X {$3 4 6 6 7 8 • » 10 ^U 13 13 i 

Figure 30. — Error curve plotted from the data given by thirty dancers, of 
diflFerent ages and under dififerent conditions of training, in white-black discrim- 
ination tests. 

the unsatisfactory as well as the satisfactory steps in my study 
of the dancer. 

The form of the white-black discrimination curve of Figure 
29 is more surprising than disappointing to me, for I had 
anticipated many more irregularities than appear. What 
I had expected, as the result of training five or even ten pairs 
of mice, was the kind of curve which is presented, for con- 
trast with the one already discussed, in Figure 30. This 
also is an error curve, but, unlike the previous one, it is based 
upon results which were got from individuals of different 
ages which were trained according to the following different 
methods. Ten of these individuals were given two or five 
tests daily, ten were given ten tests daily, and ten were given 



2 34 The Dancing Mouse 

twenty tests daily. The form of the curve serves to call at- 
tention to the importance of uniform conditions of training, 
in case the results are to be used as accurate measures of 
the rapidity of learning. 

Examination of the detailed results of the white-black 
discrimination tests as they appear in the tables of Chapter 
VII will reveal the fact that some individuals succeeded in 
choosing correctly in a series of ten tests after not more than 
five series, whereas others required at least twice as many 
tests as the basis of a perfect series. In very few instances, 
however, was a perfect habit of discrimination estabHshed 
by fewer than one hundred tests. As the averages just pre- 
sented in Table 41 indicate, fifteen series, or one hundred and 
fifty tests, were required for the completion of the experiment. 
One might search a long time, possibly, for another mammal 
whose curve of error in a simple discrimination test would 
'fall as gradually as that of the dancer. It is fair to say that 
this animal learns very slowly as compared with most mam- 
mals which have been carefully studied. It is to be remem- 
bered, however, that quantitative results such as are here 
presented for the dancer are available for few if any other 
animals except the white rat. Neither in the form of the 
curve of learning nor in the behavior of the animal as it makes 
its choice of an electric-box is there evidence of anything 
which might be described as a sudden understanding of the 
situation. The dancer apparently learns by rote. It ex- 
hibits neither intelligent insight into an experimental situa- 
tion nor abihty to profit by the experience of its companions. 
TKaTlhe selection of the white box occurs in various ways 
in different individuals, and even in the same individual at 
different periods in the training process, is the only indica- 
tion of anything suggestive of implicit reasoning. Naturally 
enough comparison of the two boxes is the first method of 



Habit Formation : Discrimination Method 235 

selection. It takes the dancers a surprisingly long time to 
reach the point of making this comparison as soon as they 
are confronted by the entrances to the two electric-boxes. 





























n 


i 






















. 


1? 


























\\ 


\ 
























10 


\ 


























\ 


























\ 






















• 


•y 




\ 






















A 




\ 


























\ 




























\ 




















a 







\ 


"-S 


























\ 
















1 














--- 




s. 












■ 












N 


^ 







Figure 31. — Curve of habit formation, plotted from the data of labyrinth-D 
tests with ten males and ten females. 

The habit of running from entrance to entrance repeatedly 
before either is entered, once having been acquired, is re- 
tained often throughout the training experiments. But in 
other cases, an individual finally comes to the point of choos- 
ing by what appears to be the immediate recognition of the 
right or the wrong box. In the former case the mouse enters the 



236 The Dancing , Mouse 

white box immediately ; in the latter, it rushes from the black 
box into the white one without hesitation. So much evi- 
dence the discrimination tests furnish of forms of behavior 
which in our fellow- men we should interpret as rational. 

Comparison of the error curves for the labyrinth tests 
(Figures 26 and 31) with those for the discrimination tests 
(Figures 29 and 30) reveals several interesting points of differ- 
ence. The former fall very abruptly at first, then with de- 
creasing rapidity, to the base line ; the latter, on the contrary, 
fall gradually throughout their course. Evidently the laby- 
rinth habit is more readily acquired by the dancer than is the 
visual discrimination habit. Certain motor tendencies can 
be established quickly, it would seem, whereas others, and 
especially those which depend for their guidance upon visual 
stimuli, are acquired with extreme slowness. From this it 
might be inferred that the labyrinth method is naturally far 
better suited to the nature of the dancer thaji is any form of 
the discrimination method. I believe that this inference is 
correct, but at the same time I am of the opinion that the 
discrimination method is of even greater value than the 
labyrinth method as a means of discovering the capacity of 
the animal for modification of behavior. 

Inasmuch as my first purpose in the repetition of white- 
black discrimination tests with a number of individuals 
was to obtain quantitative results which should accurately 
indicate individual, age, and sex differences in the rapidity 
of learning, it is important to consider the reliability of the 
averages with which we have been dealing. Possibly two 
groups of five male dancers each, chosen at random, would 
yield very different results in discrimination tests. This 
would almost certainly be true if the animals were selected 
from different lots, or were kept before and during the tests 
under different environmental conditions. But from my 



Habit Pormaiion : Discrimijiatio^t Method 237 

experiments it has become apparent that the average of the 
results given by five individuals of the same sex, age, and 
condition of health, when kept in the same environment and 
subjected to the same experimental tests, is sufficiently con- 
stant from group to group to warrant its use as an index 
of modifiability for the race. This expression, index of modi- 
fia"bility, is a convenient mode of designating the average 
number of tests necessary for the establishment of a perfect 
habit of white-black discrimination. Hereafter I shall use 
it instead of a more lengthy descriptive phrase. 

As an indication of the degree of accuracy of measurements 
of the rapidity of learning which are obtained by the use of 
5 individuals I may offer the following figures. For one of 
two directly comparable groups of 5 male dancers which were 
chosen from 16 individuals which had been trained, the num- 
ber of tests which resulted in a perfect habit of white-black 
discrimination was 92 ; for the other group it was 96. These 
indices for strictly comparable groups of 5 individuals each 
differ from one another by less than 5 per cent. Similarly, 
in the case of two groups of females, the indices of modifia- 
bility were 94 and 104. These figures designate the number 
of tests up to the point at which errors ceased for at least three 
successive series (30 tests). 

The determination of the probable error of the index of 
modifiability further aids us in judging of the reliability of 
the measure of the rapidity of learning which is obtained by 
averaging the results for 5 individuals. For a group of 5 
rnales (Table 43, p. 243) the index was 72 ± 3.5 ; and for 
a group of 5 females of the same age as the males and strictly 
comparable with respect to conditions of white-black training, 
it was 104^2.9. A probable error of ± 3.5 indicates the 
reliability of the first of these indices of modifiability; one 
of ±2.9, that of the second. 



238 The Dancing Mouse 

I do not doubt that 10 individuals would furnish a more 
reliable average than 5, but I do doubt whether the pur- 
poses of my experiments would have justified the great in- 
crease in work which the use of averages based upon so large 
a group would have necessitated. 

Further discussion of the index of modifiability may be 
postponed until the several indices which serve as measures 
of the efficiency of different methods of training have been 
presented in the next chapter. 

From the data which constitute the materials of the present 
chapter it is apparent that the results of the discrimination 
method are amenable to much more accurate quantitative 
treatment than are those of the problem method or the laby- 
rinth method. But I have done little more as yet than de- 
scribe the method by which it is possible to measure certain 
dimensions of the intelligence of the dancer, and to state some 
I general results of its application. In the remaining chapters 
it will be our task to discover the value of this method and of 
the results which it has yielded. 



CHAPTER XV 
The Efficiency of Training Methods 

The nature of the modifications which are wrought in 
the behavior of an organism varies with the method of train- 
ing. This fact is recognized by human educators, as well as 
by students of animal behavior (makers of the science of 
comparative pedagogy), but unfortunately accurate measure- 
ments of the efficiency of our educational methods are rare. 

Whatever the subject of investigation, there are two pre- 
eminently important aspects of the educative process which 
may be taken as indications of the value of the method of 
training by which it was initiated and stimulated. I refer 
to the rapidity of the learning process and its degree of per- 
manency, or, in terms of habit formation, to the rapidity 
with which a habit is acquired, and Jo its duration. Of these 
two easily measurable aspects of the modifications in which 
training results, I have chosen the first as a means to the special 
study of the efficiency of the training to which the dancing 
mouse has been subjected in my experiments. 

The reader who has followed my account of the behavior 
of the dancer up to this point will recall that in practically 
all of the discrimination experiments the number of tests in 
a series was ten. Some readers doubtless have wondered 
why ten rather than five or twenty tests was selected as the 
number in each continuous series. I shall now attempt 
to answer the question. It was simply because the efficiency 
of that number of tests, given daily, when taken in connection 

239 



240 The Dancing Mouse 

with the amount of time which the conduct of the experiments 
required, rendered it the most satisfactory number. But 
this statement demands elaboration and explanation. 

Very early in my study of the dancer, I learned that a single 
experience in a given experiment day after day had so little 
effect upon the animal that a perfect habit could not be es- 
tablished short of several weeks or months. Similarly, ex- 
periments in which two tests per day were given proved that 
even a simple discrimination habit cannot be acquired by 
'the animal under this condition of training with sufficient 
rapidity to enable the experimenter to study the formation of 
the habit advantageously. Next, ten tests in succession each 
day were given. The results proved satisfactory, consequently 
I proceeded to carry out my investigation on the basis of a 
ten-test series. After this method had been thoroughly 
tried, I decided to investigate the efficiency of other methods 
for the purpose of instituting comparisons of efficiency and 
discovering the number of tests per day whose efficiency, 
as measured by the rapidity of the formation of a white-black 
discrimination habit, is highest. 

For this purpose I carefully selected five pairs of dancers 
of the same age, descent, and previous experience, and gave 
them white-black tests in series of two tests per day (after 
the twentieth day the number was increased to five) until they 
had acquired a perfect habit of discriminating. Similarly 
other dancers were trained by means of series of ten tests, 
twenty tests, or one hundred tests per day. Since it was my 
aim to make the results of these various tests strictly com- 
parable, I spared no pains in selecting the individuals, and 
in maintaining constancy of experimental conditions. The 
order of the changes in the position of the cardboards which 
was adhered to in these efficiency tests was that given in 
Table 12. 



The Efficiency of Training Methods 241 

At the beginning of the two-test training I thought it pos- 
sible that the animals might acquire a perfect habit with only 
a few more days' training than is required by the ten-test 
method. This did not prove to be the case, for at the end of 
the twentieth day (after forty tests in all) the average number 
of mistakes, as Table 42 shows, was 3.2 for the males and 
3.0 for the females. Up to this time there had been clear 
evidence of the formation of a habit of discriminating white 
from black, but, on the other hand, the method had proved 
very unsatisfactory because the first test each day usually 
appeared to be of very different value from the second. 
On account of the imminent danger of the interruption of the 
experiment by the rapid spread of an epidemic among my 
mice, I decided to increase the number of tests in each series 
to five in order to complete the experiment if possible before 
the disease could destroy the animals. On the twenty-first 
day and thereafter, five-test series were given instead of two- 
test. Unfortunately I was able to complete the experiment 
up to the point of thirty successive correct tests with only 
six of the ten individuals whose numbers appear at the top 
of Table 42. That the results of this table are reliable, de- 
spite the fact that some of the individuals had to be taken out 
of the experiment on account of bad condition, is indicated 
by the fact that all the mice continued to do their best to 
discriminate so long as they were used. Possibly the habit 
would have been acquired a little more quickly by some of 
the individuals had they been stronger and more active. 

It should be explained at this point that the results in all 
the efficiency-of-training tables of this chapter are arranged, 
as in the previous white-black discrimination tables, in tens, 
that is, each figure in the tables indicates the number of errors 
in a series of ten tests. In all cases ^ and B mark preliminary 
series of tests which were given at the rate of ten tests per 

R 



242 



The Dancmcr Mouse 



series. The numbers in the first column of these tables 
designate groups of ten tests each, and not necessarily 
daily series. In Table 42, for example, i includes the 
results of the first five days of training, 2, of the next five 



TABLE 42 

Efficiency of Training. White-Black Tests at the Rate 
OF 2 OR 5 PER Day 



Males 


Females 


Sets 
OF 10 


80 


82 


84 


86 


88 


Av. 


73 


79 


83 


8s 


89 


Av. 


A 


5 


5 


4 


8 


5 


5-4 


5 


6 


7 


7 


6 


6.2 


B 


5 


3 


6 
6 


5 
6 


6 


5-0 


7 


5 
6 


7 
9 


6 

4 


7 
6 


6.4 


I 


7 


7 


6 


6.4 


7 


6.4 


2 


2 


I 





6 


6 


3-0 


6 


5 


6 


5 


5 


.';.4 


3 


4 


5 


4 


I 


2 


3-2 


6 


5 


2 


4 


I 


3.6 


4 


3 


4 


7 


2 





3.2 


4 


3 


I 


4 


3 


3-0 


5 


2 


3 


3 


2 


4 


2.8 


- 


3 


4 


3 


I 


2.7 


6 


2 


2 


- 


2 


2 


2.0 


- 





2 


2 





1.0 


7 


- 


I 


- 





I 


0.7 


- 


I 





2 


I 


1.0 


8 


- 


- 


- 


I 


I 


I.O 


- 


I 


I 








0-5 


9 


- 


- 


- 





I 


0-5 


- 


I 


I 








0-5 


10 


- 


- 


- 











- 

















II 


- 


- 


- 











- 















12 


- 


- 


- 










- 
















days, and so on. The table shows that No. 80 made seven 
wrong choices in- the first five series of two tests each. This 
method of grouping results serves to make the data for the 
different methods directly comparable, and at the same time 
it saves space at the sacrifice of very little valuable informa- 
tion concerning the nature of the daily results. It is to be 



The Efficiency of Training Methods 243 

noted, with emphasis, that the two-five tests per day training 
estabHshed a perfect habit after four weeks of training. This 
method is therefore costly of the experimenter's time. 

The results of the ten-test training as they appear in Table 
43 need no special comment, for quite similar data have al- 
ready been examined in other connections. In the case of 
this table it is to be remembered that each figure represents 
the number of errors for a single day as well as for a series 
of ten successive tests. The results of Table 44, on the other 



TABLE 43 

Efficiency of Training. White-Black Tests at the Rate of 

10 PER Day 





Males 


Females 


Sets 

OF 10 


210 


220 


230 


410 


420 


Av. 


215 


225 


235 


41S 


425 


Av. 


A 
B 


6 
6 


5 
8 


6 
8 

6 

I 
4 
3 
4 
4 
3 
I 





6 

5 


6 

I 

4 
3 
4 
2 

4 

I 





5-8 
5.6 


8 

8 


4 

7 


4 
6 


8 
6 

6 
2 

3 
3 
3 

I 

3 
2 

I 

I 
2 





5 
2 


5.8 
5-8 


I 
2 
3 
4 
5 
6 

7 
8 

9 
10 
II 
12 
13 
14 
15 


6 

4 
3 
5 
3 
2 
I 





7 
3 
I 


I 





2 
2 

3 
3 

I 

I 

I 





5-0 
2.6 

3-0 
2.6 
2.4 
1.6 

I.O 

0.2 

0.2 








7 
5 
3 
2 
I 
2 
I 

I 





6 
6 

3 

I 

3 
I 
I 


2 

3 





5 
4 
4 
3 
3 
I 
2 
2 

I 





4 

5 
4 
3 
3 


3 
3 
I 
2 





5.6 
4.4 

3-4 

2.4 

2.6 

1.0 

2.0 

1.4 

0.6 

1.0 

0.8 

0.4 











244 



The Daiicinz Mouse 



Efficiency of Training. 



TABLE 44 

White-Black Tests at the Rate of 
20 per Day 



Males 






Females 






Sets 

OF 10 


72 


74 


208 


240 


402 


Av. 


217 


239 


245 


403 


407 


Av. 


A 


4 


6 


7 


7 


6 


6.0 


5 


4 


7 


7 


6 


5.8 


B 


6 


4 


6 


8 


7 
5 


6.2 


7 


3 


5 


8 


5 
6 


5-6 


I 


3 


5 


7 


5 


5-0 


3 


6 


4 


4 


4.6 


2 


4 


3 


7 


5 


4 


4.6 


7 


3 


5 


4 


6 


5-0 


3 


3 


3 


3 


5 


3 


3-4 


4 


3 


3 


2 


5 


3-4 


4 


6 


3 


I 


4 


5 


3.8 


5 





I 


2 


3 


2.2 


5 


4 


I 





2 


3 


2.0 


6 








I 


2 


1.8 


6 


3 


I 





2 


2 


1.6 


4 


I 


I 





6 


2.2 


7 


3 


2 





I 


I 


1.4 


I 











I 


0.4 


8 


2 










I 


0.6 





3 


3 





2 


1.6 


9 


2 


I 




I 


I 


I.O 


I 










3 


0.8 


10 


I 


2 




I 





0.8 





I 


I 




2 


0.8 


II 


3 


I 










0.8 



















12 


I 


2 










0.6 



















13 


































14 





° 























15 






























hand, appear as subdivided series, since each daily series was 
constituted by two series of ten tests, or in all twenty tests. 

Finally, in Table 45 I have arranged the results of what 
may fairly be called the continuous training method. In 
connection with several of the labyrinth experiments of 
Chapter XIII continuous training proved very satisfactory. 
It therefore seemed worth while to ascertain whether the same 
method would not be more efficient than any other for the 



The Efficiency of Training Methods 245 

establishment of a white-black discrimination habit. That 
this method was not applied to ten individuals as were the 
two-five-test, the ten-test, and the twenty-test methods is due 
to the fact that it proved practically inadvisable to continue 
the tests long enough to complete the experiment. I have 
usually designated the method as one hundred or more 
tests daily. I applied this training method first to individuals 
Nos. 51 and 60. At the end of one hundred and twenty 
tests with each of these individuals I was forced to discontinue 
the experiment for the day because of the approach of dark- 
ness. In the table the end of a series for the day is indicated 
by a heavy line. The following day Nos. 51 and 60 succeeded 
in acquiring a perfect habit after a few more tests. 



TABLE 45 

Efficiency of Training. White-Black Tests at the Rate of 
100 OR More per Day 



Sets 

OF 10 


51' 


60 


87 


Av. 


A 


5 


5 


6 


5-3 


B 


5 


3 


7 


5-0 


I 


6 


6 


5 


5-7 


2 


3 


2 


5 


3.3 


3 


5 


4 


7 


5-3 


4 


7 


4 


5 


5-3 


5 


6 


2 


3 


3.7 


6 


I 


I 


3 


1-7 


7 


4 


2 


3 


3-0 


8 


3 


3 





2.0 


9 


2 


2 


3 


2.3 


10 


5 





2 


2.3 


II 


I 


2 


2 


1.7 



Sets 
OF 10 


SI 


60 


87 


Av. 


12 


2 


I 


I 


1.3 


13 


4 


I 


2 


2.3 


14 


I 


2 


I 


1-3 


15 


3 


I 


5 


3-0 


16 


3 


3 


2 


2.7 


17 


I 


^ 


I 


0.7 


18 


2 


° 


I 


I.O 


19 








2 


0.7 


20 













21 







I 


0.3 


22 






- 




23 






- 




24 






— 





* Age of No. 51, 22 weeks. Age of No. 60, 17 weeks. Age of No. 87, 
weeks. 



246 The Dancing Mouse 

The results of the continuous training method for these 
two mice were so strikingly different from those yielded by 
the other methods that I at once suspected the influence of 
some factor other than that of the number of tests per day. 
The ages of Nos. 51 and 60 at the time of their tests were 
twenty-two and seventeen weeks, respectively, whereas all 
the individuals used in connection with the other efficiency 
tests were four weeks of age. It seemed possible that the 
slow habit formation exhibited in the continuous training 
experiments might be due to the greater age of the mice. I 
therefore selected a healthy active female which was only 
eight weeks old, and tried to train her by the continuous 
training method. With this individual. No. 87, the results 
were even more discouraging than those previously obtained, 
for she was still imperfect in her discrimination at the end of 
two hundred and ten tests. At that point the experiment 
was interrupted, and it seemed scarcely worth while to con- 
tinue it further at a later date. The evidence of the extremely 
low efficiency of the continuous method in comparison with 
the other methods which we have been considering is so con- 
clusive that further comment seems superfluous. 

We are now in a position to compare the results of the 
several methods of training which have been applied to the 
dancer, and to attempt to get satisfactory quantitative ex- 
pressions of the efficiency of each method. I have arranged 
in Table 46 the general averages yielded by the four methods. 
Although these general results hide certain important facts 
which will be exhibited later, they clearly indicate that an 
increase in the number of tests per day does not necessarily 
result in an increase in the rapidity of habit formation. 
Should we attempt, on superficial examination, to interpret 
the figures of this table, we would doubtless say that in effi- 
ciency the two-five-test method stands first, the continuous- 



The Efficiency of Trainmg Methods 247 

test method last, while the ten-test and twenty-test methods 
occupy intermediate positions. 

TABLE 46 

Efficiency of Training 

Number of Errors in White-Black Series for Different Methods of 

Training 



SETS OF lO 


2 OR 5 Tests 
PER Day 


10 Tests 
PER Day 


20 Tests 
PES Day 


icx) OR More 
Tests per Day 


A 


5-8 


5-8 


5-9 


5-3 


B 


5-7 


5-7 


5-9 


5-0 


I 


6.4 


5-3 


4.8 


5-7 


2 


4.2 


3.5 


4.8 


3-3 . 


3 


3.4 


3.2 


3-4 


5-3 


4 


3-1 


2-5 


3-0 


5-3 


5 


2.7 


2.5 


1.9 


3-7 


6 


1-5 


1-3 


1.9 


1.7 


7 


0.9 


1-5 


0.9 


3-0 


8 


0.7 


0.8 


I.I 


2.0 


9 


0.5 


0.4 


0.9 


2.3 


10 





0-5 


0.8 


2.3 


II 





0.4 


0.4 


1-7 


12 





0.2 


0.3 


1.3 


13 










2.3 


14 










1.3 


15 










3.0 


16 








2.7 


17 








0.7 


18 








I.O 


19 








0.7 


20 












We may now apply to the results of our efhciency-of-train- 
ing tables the method of measuring efficiency which was 
mentioned at the end of the preceding chapter as the index 



248 



The Dancing Mouse 



of modifiabilUy (that number oj tests after which no errors occur 
for at least thirty tests). By taking the average number of tests 
for the several individuals in each of the Tables 42, 43, 44, 
and 45 we obtain the following expressions of efficiency: — 



Method 

Two-five-test 
Ten-test . 
Twenty-test 
Continuous-test 



Index of Modifiability (Efficiency) 

81.7 ±2.7 
88.0 ±4.1 

• 91-0 ±5-3 
. 170.0 ± 4.8 



Since the difference between the indices for the ten-test and 
the twenty-test methods lies within the limits of their probable 
errors (±4.1 and ±5.3) it is evident that it is not significant. 
Except for this, I think these indices may be accepted 
as indications of real differences in the value of the several 
methods of training. 

A somewhat different interpretation of our results is sug- 
gested by the grouping of individuals according to sex. In 
Table 47 appear the general averages for the males and the 
females which were tested by the several methods. The most 
striking fact exhibited by this table is that of the high efficiency 
of the twenty-test method for the females. Apparently 

TABLE 47 
Efficiency of Training 





Males 


Females 


Condition 


Index of Modifiability 


Index of Modifiability 


2 or 5 tests per day 
10 tests per day 
20 tests per day 
100 or more tests per day 


85.0 

72.0 

94.0 

160.0 


80.0 
104.0 

88.0 
180.0 



The Efficiency of Training Ale t hods 249 

they profited much more quickly by this method than by 
the ten-test method, whereas just the reverse is true of the 
males. I present the data of this table merely to show that 
general averages may hide important facts. 

From all considerations that have been mentioned thus 
far the reader would be justified in concluding that I made a 
mistake in selecting the ten-test method for my study of the 
modifiability of the behavior of the dancer. That this con- 
clusion is not correct is due to the time factor in the experi- 
ments. If the dancer could acquire a perfect habit as a 
result of twelve days' training, no matter whether two, five, 
ten, or twenty tests were given daily, it would, of course, be 
economical of time for the experimenter to employ the two- 
test method. But if, on the contrary, the two-test method 
required twice as many days' training as the five-test method, 
it would be economical for him to use the five-test method 
despite the fact that he would have to give a larger number 
of tests than the two-test method would have demanded. 
In a word, the time which the work requires depends upon 
the number of series which have to be given, as well as upon 
the number of tests in each series. As it happens, the ten- 
test method demands less of the experimenter's time than 
do methods with fewer tests per day. The twenty-test 
method is even more economical of time, but it has a fatal 
defect. It is at times too tiresome for both mouse and man. 
These facts indicate that a balance should be struck between 
number of tests and number of series. The fewer the tests 
per day, within the limits of two and one hundred, the higher 
the efficiency of the method of training, as measured in terms 
of the total number of tests necessary for the establishment 
of a perfect habit, and the lower its efficiency as measured in 
terms of the number of series given. The greater the number 
of tests per day, on the other hand, the higher the efficiency 



250 The Dancing Mouse 

of the method in terms of the number of series, and the lower 
its efficiency in terms of the total number of tests. By taking 
into account these facts, together with the fact of fatigue, 
we are led to the conclusion that ten tests per day is the most 
satisfactory number. 

If my time and attention had not been fully occupied with 
other problems, I should have determined the efficiency of 
various methods of training in terms of the duration of habit, 
as well as in terms of the rapidity of its formation. As these 
two measures of efficiency might give contradictory results, 
it is obvious that a training method cannot be fairly evaluated 
without consideration of both the rapidity of habit formation 
and the permanency of the habit. A priori it seems not im- 
probable that slowness of learning should be directly cor- 
related with a high degree of permanency. By the further 
application of the method which I have used in this study 
of the efficiency of training we may hope to get a definite 
answer to this and many other questions concerning the 
nature of the educative process and the conditions which 
influence it. 



CHAPTER XVI 
The Duration of Habits : Memory and Re-learning 

The effects of training gradually disappear. Habits wane 
with disuse. In the dancer, it is not possible to establish 
with certainty the existence of memory in the introspective 
psychological sense ; but it is possible to measure the efficiency 
of the training to which the animal is subjected, and the degree 
of permanency of habits. The materials which constitute 
this chapter concern the persistence of unused habits, and 
the influence of previous training on the re-acquisition of a 
habit which has been lost or on the acquisition of a new habit. 
For convenience of description, I shall refer to certain of the 
facts which are to be discussed as facts of memory, with the 
clear understanding that consciousness is not necessarily 
implied. By memory, wherever it occurs in this book, I 
mean the ability of the dancer to retain the power of adaptive 
action which it has acquired through training. 

I first discovered memory in the dancer, although there was 
previously no reason for doubting its existence, in connection 
with the ladder-climbing tests of Chapter XII. In this ex- 
periment two individuals which had perfectly learned to escape 
from the experiment box to the nest-box by way of the wire 
ladder, when tested after an interval of two weeks, during 
which they had remained in the nest-box without opportunity 
to exercise their newly acquired habit, demonstrated their 
memory of the method of escape by returning to the nest-box 
by way of the ladder as soon as they were given opportunity 

251 



252 The Dancing Mouse 

to do so. As it did not lend itself readily to quantitative 
study, no attempts were made to measure the duration of 
this particular habit. At best the chmbing of a wire ladder 
is of very uncertain value as an indication of the influence of 
training. 

Similarly, the persistence of habits has been forced upon 
my attention day after day in my various experiments with 
the mice. It is obvious, then, that the simple fact of memory 
is well established, and that we may turn at once to an exami- 
nation of the facts revealed by special memory and re-learning 
experiments. 

The visual discrimination method, which proved invalu- 
able as a means of measuring the rapidity of habit formation, 
proved equally serviceable in the measurement of the per- 
manency or duration of habits. Memory tests for discrimi- 
nation habits were made as follows. After a dancer had 
been trained in the discrimination box so that it could choose 
the correct electric-box, white, red, blue, or green as it might 
be, in three successive daily series of ten tests each, it was 
permitted to remain for a certain length of time without 
training and without opportunity to exercise its habit of 
visual discrimination and choice. At the expiration of the 
rest interval, as we may designate the period during which 
the habit was not in use, the mouse was placed in the dis- 
crimination box under precisely the same conditions in which 
it had been trained and was given a series of ten memory 
tests with the box to be chosen alternately on the right and 
on the left. In order that the entire series of ten tests, and 
sometimes two such series given on consecutive days, might 
be available as indications of the duration of a habit, the 
mouse was permitted to enter and pass through either of the 
electric-boxes without receiving a shock. Had the shock 
been given as punishment for a wrong choice, it is obvious 



The Duration of Habits 253 

that only the first test of the memory series would be of value 
as an indication of the existence of a previously acquired 
habit. Even under the conditions of no shock and no stop 
or hindrance the first test of each memory series is of pre- 
eminent importance, for the mouse tends to persist in choos- 
ing either the side or the visual condition (sometimes one, 
sometimes the other) which it chooses in the first test. If 
the wrong box is chosen to begin with, mistakes are likely to 
continue because of the lack of punishment ; in this case the 
animal discriminates, but there is no evidence that it re- 
members the right box. Likewise, if the right electric-box 
is chosen in the first test, correct choices may continue 
simply because the animal has discovered that it can safely 
enter that particular box; again, the animal discriminates 
without depending necessarily upon its earHer experience. I 
have occasionally observed a series of ten correct choices, 
made on the basis of an accidental right start, followed by 
another series in which almost every choice was wrong, be- 
cause the animal happened to start wrong. 

As the results of my tests of memory are of such a nature 
that they cannot advantageously be averaged, I have arranged 
in Table 48 a number of typical measurements of the duration 
of visual discrimination habits. In this table I have indi- 
cated the number and age of the individual tested, the habit 
of discrimination which had been acquired, the length of 
the rest interval, the result of the first test (right or wrong), 
and the number of errors made in each series of ten memory 
tests. 

This quantitative study of the duration of simple habits of 
choice showed that in the majority of cases a perfectly ac- 
quired habit persists for at least two weeks. To be perfectly 
fair to the animal I must restrict this statement to visual 
conditions other than colors, for the dancer exhibited little 



254 



The Dancing Mouse 



TABLE 48 

Measurements of the Duration of a Habit 

Memory 





Age 


Name of Test 


Rest 
Interval 


First 
Choice 


Errors 


No. 


First 


Second 












Series 


Series 


1000 


25 weeks 


White-black 


4 weeks 


Right 







5 


27 


White-black 


4 


Right 


5 


7 


210 


15 


White-black 


8 


Right 


S 




220 


15 


White-black 


8 


Right 


4 




230 


IS 


White-black 


8 


Wrong 


S 




215 


IS 


White-black 


8 


Right 


5 




225 


15 


White-black 


8 


Right 


2 




235 


15 


White-black 


8 


Right 


7 




410 


IS 


White-black 


8 


Wrong 


4 




415 


IS 


White-black 


8 


Wrong 


6 




420 


15 


White-black 


8 


Wrong 


3 




425 


IS 


White-black 


8 


Right 


3 




2 


28 


Black-white 


4 


Wrong 


9 




7 


17 


Black-white 


2 


Wrong 


I 




7 


21 


Black-white 


6 


Right 


I 




7 


27 


Black-white 


10 


Right 


I 


6 


998 


18 


Black-white 


2 


Wrong 


3 




998 


22 


Black-white 


4 


Right 







998 


28 


Black-white 


10 


Right 


S 


S 


13 


10 


Black-white 


4 


Right 


3 




14 


10 


Black-white 


4 


Right 


3 




15 


10 


Black-white 


4 


Right 


2 




16 


10 


Black-white 


4 


Right 


4 




ICKDO 


2S 


Light blue-orange 


4 


Right 


4 




2 


28 


Light blue-orange 


2 


Wrong 


S 




5 


28 


Light blue-orange 


6 


Wrong 


4 


6 


3 


2S 


Light blue-orange 


4 


Wrong 


8 




10 


24 


Light blue-orange 


2 


Right 


8 




10 


26 


Light blue-orange 


2 


Right 


S 




II 


2S 


Light blue-orange 


2 


Right 


6 




II 


27 


Light blue-orange 


2 


Wrong 


S 




151 


13 


Green-red 


2 


Right 


I 





152 


13 


Green -red 


2 


Right 


5 


I 



The Duration of Habits 255 

ability either to acquire or to retain a habit of distinguishing 
spectral colors. Altogether, I made a large number of white- 
black and black-white memory tests after rest intervals of 
four, six, eight, or ten weeks. The results for the four-week 
interval show extreme individual differences in memory. Num- 
ber 1000, for example, was able to choose correctly every time 
in a series of white-black tests after a rest interval of four 
weeks, whereas No. 5 was wrong as often as she was right 
after the same interval. I have placed the results for these 
two individuals at the head of the table because they suggest 
the variations which render averages undesirable. Number 
1000 had a perfect habit at the end of four weeks of disuse ; 
No. 5 had no habit whatever. I shall reserve further discus- 
sion of age, sex, and individual differences in the permanency 
of habits for the next chapter. 

With Nos. 7 and 998 memory tests were made after three 
different rest intervals. At the end of two weeks the black- 
white habit was present in both individuals, although it was 
not perfect. After six and four weeks, respectively (see 
Table 48), it still persisted ; in fact, it apparently had im- 
proved as the result of additional training after the earlier 
memory tests. At the expiration of ten weeks it had wholly 
disappeared. In her first series of memory tests after the 
ten- week interval No. 7 made only one error, but a chance 
choice of the black (right) in the first test and the subsequent 
choice of the box in which no shock had been received serve 
to account for results which at first appear to be indicative 
of memory. That this explanation is correct is proved by 
the fact that a second memory series, in which the first choice 
happened to be wrong, resulted in six mistakes. Evidently 
she had lost the habit. 

In no instance have memory tests definitely indicated the 
presence of a habit after a rest interval of more than eight 



256 The Dancing Mouse 

weeks. It is safe, therefore, to conclude from the resuhs 
which have been obtained that a white-black or black-white 
discrimination habit may persist during an interval of from 
two to eight weeks of disuse, but that such a habit is seldom 
perfect after more than four weeks. 

The measurements of memory which were made in con- 
nection with color discrimination experiments are markedly 
different from those which were obtained in the brightness 
tests. As might have been anticipated (?), in view of the 
extreme difficulty with which the dancer learns to discrimi- 
nate colors, the habit of discriminating between qualitatively 
different visual conditions does not persist very long. I have 
never obtained evidence of a perfect habit after an interval 
of more than two weeks, and usually, as is apparent from 
Table 48, the tests indicated very imperfect memory at the 
end of that interval. It seems probable that even in these 
so-called color tests discrimination is partly by brightness 
difference, and that the imperfection of the habit and its 
short duration are due to the fact that the basis of discrimi- 
nation is inadequate. This is the only explanation which I 
have to offer for the difference which has been demonstrated 
to exist between the duration of brightness discrimination 
habits and color discrimination habits. 

The duration of a discrimination habit having been meas- 
ured with a fair degree of accuracy, I undertook the task of 
ascertaining whether training whose results have wholly 
disappeared, so far as memory tests are in question, influences 
the re-acquisition of the same habit. Can a habit be re-ac- 
quired with greater facility than it was originally acquired ? 
Is re-learning easier than learning? To obtain an answer 
to the question which may be asked in these different forms, 
ten individuals were experimented with in accordance with 
a method whose chief features are now to be stated. In 



The Duration of Habits 



257 



each of these ten individuals a perfect white-black habit was 
established by the use of the standard series of tests the order 
of which is given in Table 12. At the expiration of a rest 
interval of eight weeks precisely the same series of tests were 
repeated as memory and re-training tests. In this repetition, 



7 


































■■ — 


>v 
































\ 
\ 


























. 






\ 






<_ 


















. 










\ 

\ 

> 


^--. 


N 




\, 
































N 




\, 


























^"»^ 




^^^ 


> 


'^^ 














— -, 





---"' 



\ B 1 2 3 4 5; -6 7 » 9 10 il 12 13 14 

Figure 32. — Error curves plotted from the data given by ten dancers in white- 
black discrimination tests. The solid line ( ) is the error curve of the origi- 
nal learning process ; the broken line ( )is that of the re-learning process, 

after an interval of eight weeks. 

the preliminary series, A and -B, served as memory tests, 
and the subsequent training series, as re-training series. 

The striking results of this investigation of re-learning are 
exhibited in the curves of learning and re-learning of Figure 
32. These curves make it appear that the mice re-acquired 
the white-black discrimination habit much more readily than 
they had originally acquired it. But in addition to furnishing 
the basis for some such statement as the foregoing, the curves 
suggest a serious criticism of the experiment. 

In the original tests, the preliminary series indicated a 
strong preference for black. In series A it was chosen on the 
average 5.8 times in 10, and in series B, 5.7 times. This 
preference was rapidly overcome by the training series, and 



258 The Dancing Mouse 

at the end of 130 tests discrimination was perfect. All this 
appears, in the curve of learning (solid line of figure). On 
the other hand, these preliminary series when repeated as 
memory tests, after a rest-interval of eight weeks, gave mark- 
edly different results. Series A indicated preference for 
white (5.6 times in 10) instead of black, and series B indicated 
only a slight preference for black. In brief, series A and B 
show that the preference for black was considerably stronger 
at the beginning of the training than at the beginning of the 
re-training. 

In the light of these facts it is fair to claim that the effects 
of the white-black training had not wholly disappeared as 
the result of eight weeks of rest, and that the experiment 
therefore fails to furnish satisfactory grounds for the state- 
ment that re-learning occurs more rapidly than learning. 
I accept this criticism as pertinent, although not necessarily 
valid, and at the same time I freely admit that the results 
have a significance which I had not anticipated. But they 
are not less interesting or valuable on that account. Grant- 
ing, then, that at least some of the ten individuals which took 
part in the experiment had not completely lost the memory 
of their white-black training at the end of eight weeks, it is 
still possible that an examination of the individual results 
may justify some conclusion concerning the question which 
was proposed at the outset of the investigation. Such an 
examination is made possible by Tables 49 and 50, in which 
I have arranged separately the results for the males and the 
females. 

Only three of the ten individuals failed to re-acquire the 
habit of white-black discrimination more quickly than it 
had originally been acquired, and, in the case of these excep- 
tions, No. 220 required exactly the same number of tests in 
each case, and No. 420 was placed at a slight disadvantage 



The Duratio7i of Habits 



259. 



TABLE 49 

White -Black Training. Ten Tests per Day 

Males 



Training 


Re-training 




210 


220 


230 


410 


420 


Av. 


210 


220 


230 


410 


420 


Av. 


A 


6 


5 


6 


6 


6 


5-8 


5 


4 


5 


4 


3 


4.2 


B 


6 


8 


8 


5 


I 


5-6 


8 


4 


5 


4 


6 


5-4 


I 


6 


7 


6 


2 


4 


5-0 


3 


3 


4 


7 


3 


4.0 


2 


4 


3 


I 


2 


3 


2.6 


2 


4 


2 


5 


3 


3.2 


3 


3 


I 


4 


3 


4 


3-0 


I 


4 


I 


4 


I 


2.2 


4 


5 





3 


3 


2 


2.6 





I 





I 


2 


0.8 


5 


3 





4 


I 


4 


2.4 





2 





2 





0.8 


6 


2 


I 


4 





I 


1.6 





I 








2 


0.6 


7 


I 





3 


I 





I.O 


















8 








I 








0.2 












I 


0.2 


9 











I 





0.2 

















10 


























I 


0.2 


II 































12 






























13 




























14 


























15 



























in the re-learning series by an interruption of the training 
between the seventh and the eighth series. Had his training 
been completed by the sixth series he too would have had the 
same number of tests in training and re-training. More- 
over, and this is of preeminent importance for a fair inter- 
pretation of the results, in several instances even those 
individuals which exhibited as strong a preference for the 
black in the memory series as in the preliminary series 
re-learned more quickly than they had learned. Number 



26o 



Th 



le 



Dancinc Mouse 



TABLE 50 

White -Black Training. Ten Tests per Day 

Females 



Training 


Re-training 




215 


225 


235 


415 


425 


Av. 


215 


225 


235 


4t5 


425 


Av. 


A 
B 


8 
8 


4 

7 


4 
6 


8 
6 


5 
2 


5.8 

5-8 


5 
8 


2 

5 


7 
6 


6 

4 


3 
3 


4.6 

5-2 


I 
2 
3 
4 
5 
6 

7 
8 

9 
10 
II 
12 
13 
14 
15 


7 
5 
3 
2 
I 
2 
I 

I 





6 
6 

3 

I 

3 
I 
I 


2 

3 





5 
4 
4 
3 
3 
I 
2 
2 

I 





6 
2 

3 
3 
3 

I 

3 
2 
I 

I 
2 





4 

5 

: 

3 


3 
3 
I 
2 





5-6 

4.4 

3-4 
2.4 
2.6 

I.O 

2.0 

1.4 

0.6 

1.0 

0.8 

0.4 








4 
I 
I 





I 

I 





5 
I 

3 

3 

died 


4 
2 
6 

3 
2 
I 

I 





3 
3 


I 





3-4 
1.6 
2.0 
1.4 

0-5 

0.2 



0.2 









210, for example, although he gave no evidence of memory, 
and, in fact, chose the black more frequently in the memory 
series than he did in the preliminary series, re-acquired the 
discrimination habit in less than half the number of tests 
which had been necessary for the establishment of the habit 
originally. 

The facts which have been presented thus far become more 
significant when the indices of modifiability for the learning 
and the re -learning processes are compared. 



The Duration of Habits 261 

Indices of Modifiability 

Learning Re-learning 

Females 104 42.5 

Males 72 54 

The behavior of the mice in the experiments, the detailed 
results of Tables 49 and 50, and the indices of modifiabihty 
together justify the following conclusions. Most of the ten 
dancers, at the end of a rest interval of eight weeks, had so 
far lost the habit of white-black discriniination that memory 
tests furnished no conclusive evidence of the influence of 
previous training ; a few individuals seemed to possess traces 
of the habit after such an interval. In the case of each group 
of individuals re-training brought about the establishment of 
a perfect habit far more quickly than did the original train- 
ing. This suggests the existence of two kinds or aspects 
of organic modification in connection with training; those 
which constitute the basis of a definite form of motor activity, 
and those which constitute the bases or dispositions for the 
acquirement of certain types of behavior. There are several 
indications that further study of the modifiability of behavior 
will furnish the facts which are necessary to render this 
suggestion meaningful. 

Closely related to the facts which have been revealed by 
the re-training experiments are certain results of the labyrinth 
experiments. For the student of animal behavior, as for the 
human educator, it is of importance to learn whether one kind 
of training increases the efficiency of similar forms of training. 
Can a dancer learn a given labyrinth path the more readily 
because it has previously had experience in another form of 
labyrinth ? 

The answer to this question, which my experimental results 
furnish, is given in Table 51. In the upper half of the table 



262 



The Dancing Mouse 



have been arranged the results for six individuals which w^ere 
trained first in labyrinth B, then in labyrinth C, and finally 
in labyrinth D. Belov^, in similar fashion, are given the re- 
sults for six individuals which were trained in the same three 
labyrinths in the order C, B, D, instead of B, C, D. My pur- 
pose in giving the training in these two orders was to ascertain 
whether labyrinth C, which had proved to be rather difficult 



TABLE 51 

The Inpluence of One Labyrinth Habit xn>ON the Formation 

OF Another 





Labyrinth B 


Labyrinth C 


Labyrinth D 


No. 


No. OF Fl!?ST 

Correct Test 


No. OF 

Last of 
Five Cor- 
rect Tests 


No. OF 

First Cor- 
rect Test 


No. OF 

Last of 
Five Cor- 
rect Tests 


No. OF 
First 

CORPECT 

Test 


No. OF Last of 

Two Correct 

Tests 


76 
78 

86 

75 
77 
87 


8 
5 

13 
4 
7 

12 


14 
20 

22 

15 
II 
22 


3 
6 

5 

8 

II 

9 


19 
14 
12 

19 
29 
20 


4 
4 
3 
4 
II 

4 


7 
5 

9 
13 
12 

9 


Av. 


8.2 


17-3 


7.0 


18.8 


5-0 


9.2 


Labyrinth C 


Labyrinth B 


Labyrinth D 


58 
60 

88 
49 

57 
85 


16 
17 
25 
34 
15 
II 


35 
18 


2 
13 

9 

I 

3 
2 


14 

37 
22 

5 

20 
II 


7 
10 

4 

7 
3 
3 


10 

14 
8 
8 
6 

4 


Av. 


19.7 


26.5 


5-0 


18.2 


5-7 


8.3 



The Duration of Habits 263 

for most individuals, would be more easily learned if the train- 
ing in it were preceded by training in labyrinth B. 

The results are sufficiently definite to warrant the conclu- 
sion that experience in B rendered the learning of C easier 
than it would have been had there been no previous labyrinth 
training. Those individuals whose first labyrinth training 
was in C made their first correct trip as the result of 19.7 
trials, whereas those which had previously been trained in 
labyrinth B were able to make a correct trip as the result of 
only 7.0 trials. Similarly the table shows that training in 
C rendered the subsequent learning of B easier. To master 
B when it was the first labyrinth required 8.2 trials ; to master 
it after C had been learned required only 5 trials. In addi- 
tion to proving that the acquisition of one form of labyrinth 
habit may facilitate the acquisition of others, comparison of 
the averages of Table 51 furnishes evidence of the truth of 
the statement that no results of training can be properly 
interpreted in the absence of knov/ledge of the previous 
experience of the organism. 



CHAPTER XVII 

Individual, Age, and Sex Differences in Behavior 

All dancers are alike in certain important respects, but 
to the trained observer of animal behavior their individual 
peculiarities are quite as evident, and even more interesting 
than their points of resemblance. Omitting consideration 
of the structural marks of individuality, we shall examine 
the individual, age, and sex differences in general behavior, 
rapidity of learning, memory, and discrimination, which have 
been revealed by my experiments. Observations which bear 
on the subject of differences are scattered through the pre- 
ceding chapters, but in no case have they been given sufficient 
prominence to force them upon the attention of those who 
are not especially interested in individual peculiarities. It 
has seemed worth while, therefore, to assemble all the avail- 
able material in this chapter for systematic examination and 
interpretation. 

In the pages which follow, individual, age, and sex pecul- 
iarities are discussed in turn. Within each of these three 
groups of differences I have arranged in order what Roy^e 
has appropriately named the facts of discriminating sen- 
sitiveness, docility, and initiative. Individuals of the same 
age and sex no less than those which differ in sex or age ex- 
hibit important differences in ability to discriminate among 
sense impressions ("discriminative sensitiveness"), in ability 
to_^profit by experience ("docility"), and in abihty to try new 
kinds of behavior ("initiative"). 

264 



Differences in Behavior 265 

Individual differences in sensitiveness to visual, auditory, 
tactual, and olfactory stimuli have been revealed by many 
of my experiments. The brightness discrimination tests 
conclusively proved that a degree of difference in illumination 
which is easily detectable by one dancer may be beyond the 
discriminating sensitiveness of another. Both the tests with 
gray papers and those with the Weber's law apparatus fur- 
nished striking evidence of individual differences in the kind 
of visual sensitiveness which throughout this book has been 
called brightness vision. I suspect that certain of the differ- 
ences which were observed should be referred to the experi- 
ence of the individuals rather than to the capacity of the visual 
organs, for training improves visual discrimination to a much 
greater extent than would ordinarily be thought possible. To 
the truth of this statement the results of the Weber's law 
experiments with No. 51 bear witness. Likewise in color 
discrimination there are individual differences, examples of 
which may be discovered by the examination of the results 
given in Chapters IX and X. 

No differences in auditory sensitiveness appeared in my 
adult dancers, for in none of them was there definite response 
to sounds, but among the young individuals di fferenc es were 
prominent. I may call attention to the data on this subject 
wKicH Table 5, p. 89, contains. The mice in four out of 
twelve litters gave no indications of hearing any sounds that 
I was able to produce; the remaining individuals responded 
with varying degrees of sensitiveness. I made no attempt 
to measure this sensitiveness, but it obviously differed from 
mouse to mouse. I feel justified, therefore, in stating that 
the young dancers exhibit extreme individual difference in 
sensitiveness to sounds. 

My observations of differences in sensitiveness to other 
forms of stimulation were made in connection with training 



266 The Dancing Mouse 

tests, and although they are not quantitative, I venture to 
call attention to them. Indeed, I am led by the results of 
j my study of various aspects of the dancer's behavior to con- 
I elude that the race exhibits individual differences in discrim- 
1 inating sensitiveness to a far greater extent than do most 
I mammals, not excepting man. The importance of this fact 
(for I am confident that any one who carefully examines the 
detailed results of the various experiments v^hich are de- 
scribed in this book v^ill agree that it is an established fact) 
cannot be overlooked. It alters our interpretation of the 
results of training, memory, heredity, and discrimination 
experiments, and it leads us to suspect that the dancing race 
is exceedingly unstable. I do not venture to make compari- 
son of my own observations of the dancer's sense equipment 
with those of Cyon, Rawitz, Zoth, and Kishi, for the differences 
are too great in many instances to be thought of as other than 
species or variety peculiarities. It has seemed fairer to com- 
pare only individuals of the same breed, or, as I have done 
and shall continue to do throughout this chapter, of two lines 
( of descent. 

With respect to docility individual differences are prominent. 
We need only turn to the various tables of results to' discover 
that in m^difi^litxpf behavior, in memory, in re-leaming, 
not to mention other aspects of docility, dancers of the same 
sex and age differed strikingly. Let me by way of illustra- 
tion cite a few cases of difference in docility. Number looo 
learned to discriminate white from black more quickly and 
retained his habit longer than any other dancer with which 
I have experimented. I should characterize him as an excep- 
tionally docile individual. Table 44 offers several examples. 
Numbers 403 and 407, though they were born in the same 
litter and were alike in appearance and in conditions of life, 
acquired the white-black habit with a difference in rapidity 



Differences in Behavior 267 

which is expressed by the indices of modifiability 50 and 100. 
In other words, it took No. 407 twice as long to acquire this 
habit as it took No. 403. Similarly the ladder-climbing tests 
revealed important individual differences in ability to profit 
by experience. In the tables of labyrinth tests (38, 39, 40) 
individual differences are too numerous to mention. It 
required forty-nine tests to establish in No. 50 a labyrinth-C 
habit which was approximately equal in degree of perfection 
to that which resulted from twenty-two tests in the case of 
No. 52. . The figures in this and other instances do not ex- 
aggerate the facts, for repeatedly I have tested individuals 
of the same litter, the same sex, and, so far as I could judge, 
of the same stage of development, and obtained results which 
differ as markedly as do those just cited. If space limits 
permitted, I could present scores of similar differences in 
docility which the problem, labyrinth, and discrimination 
methods have revealed. 

In examining the detailed individual results of the various 
tables for differences of this sort, it is important to bear in 
mind that sex, age, and descent should be taken into account, 
for with each of them, as will be shown clearly later in 
this chapter, sensitiveness, docility, and initiative vary. I 
have therefore based my statements concerning individual 
differences in docility upon the results of comparison of mice 
of the same litter, sex, and age. It is sa fe to say that human 
beings similarly selected for comparison do not exhibit greater 
differences in ability to profit by experience than did these 
dancing mice. 

The facts concerning individual differen ces in initiativ e/ 
which I have discovered are not less definite than those or 
the preceding paragraphs. From the beginning of my study 
of the dancer I observed that what one individual would 
readily learn of his own initiative another never learned. For 



268 The Dancing Mouse 

example, in the ladder-climbing experiment No. looo dis- 
tinguished himself for his initiative, whereas Nos. 4 and 5 
never acquired the habit of escaping from confinement by 
using the ladder. I noticed, in this test of the animal's ability 
to learn, that while one individual would be scurrying about 
trying all ways of escape, investigating its surroundings, 
looking, sniffing, and dancing by turns, another would de- 
vote all its time to whirling, circling, or washing itself. One 
in the course of its activity would happen upon the way of es- 
cape, the other by reason of the limited scope of its activity, 
not the lack of it, would fail hour after hour to discover even 
the simplest way of getting back to its nest, to food, and to 
its companions. Hundreds of times during the past three 
years I have noticed important individual differences in ini- 
tiative in connection with the discrimination experiments. 
The swinging wire doors which one dancer learned to push 
open before he had been in the box five minutes, another might 
not become familiar with through his own initiative for hours 
or days. In fact, it was not seldom that I had to teach an in- 
dividual to pass from one compartment to the other by gently 
pushing him against the door until it opened sufficiently 
to allow him to squeeze through. Occasionally a mouse 
learned to pull the doors open so that he could pass through 
the openings in either direction with facility. This was a 
form of individual initiative which I had not anticipated 
and did not especially desire, so I did not encourage its de- 
velopment, but, nevertheless, at least one fourth of the mice 
which I experimented with in the discrimination box learned 
the trick. The other three fourths, ahhough they were used 
in the box day after day sometimes for weeks, never discovered 
that they might return to the nest-box by pulling the swing- 
door through which they had just passed as well as by enter- 
ing one of the electric-boxes. 



Differences in Behavior 269 

Another indication of individual initiative in action ap- 
peared in the tendency of certain mice to cHmb out of the 
experiment boxes or labyrinths. It would have been ex- 
tremely easy for any of the mice to escape from the labyrinths 
by scaling the walls of the alleys, for they were only 10 cm. 
in height, and when a dancer stood on its hind legs it could 
easily reach the top with its nose. But, strange though it 
will seem to any one who has not worked with the dancer, 
not more than one in ten of the animals which I observed 
made any attempt to escape in this manner. They lacked 
initiative. That it was not due to a lack of the power to 
climb, I abundantly demonstrated by teaching a few individ- 
uals that a scramble in one corner meant easy escape from 
the maze of paths. I do not think any one of the mice was 
physically incapable of climbing, but I am confident that they 
differed markedly, not only in the wilhngness to try new modes 
of action, but in the readiness with which they could climb. 
I have already said that individuals differ noticeably in the 
scope of their activity. By this statement I mean that they 
try a varying number of kinds of activity. As in the case 
of men, so in mice, one individual will do a greater number 
of things in a few hours than another will in weeks or months. 
The dancers differ in versatility, in individual initiative, as 
do we, albeit not so markedly. 

Important differences which may with certainty be de- 
scribed as asje differences are not so obvious as are such marks 

o . ... . .. .__ ... 

of individuality as have been set forth in the preceding pages. 
I have noted few changes in discriminative sensitiveness, 
other than those with regard to auditory sensitiveness, which 
could be correlated with age. In certain instances adults 
appeared to be able to discriminate more accurately and more 
easily than young mice, but it is difficult to say whether this 
change belongs under sensitiveness or dociHty. I have not 



270 The Dancing Mouse 

made an ontogenetic study of the senses, and I am therefore 
unable to describe in detail the course of their development 
and decline. Of one important fact I am certain, that dis- 
criminative sensitiveness increases up to a certain point with 
age and with training. 

Differences in docility which are obviously to be correlated 
with age abound. In the prime of its life (from the second 
to the tenth month) the dancer is active, full of energy, quick 
to learn ; in its senility (during the second year) it is inactive, 
but at times even more docile than during the period of 
greatest physical development. Frequently I have noticed 
in connection with labyrinth tests that individuals of the age 
of a year or more learn much more quickly than do individuals 
of the age of two or three months. But, on the other hand, 
I have contradictory observations, for now and then I ob- 
tained just the opposite result in experiments to test docility. 
Evidently this is a matter which demands systematic, quan- 
titative investigation. Casual observation may suggest con- 
clusions, but it will not justify them. 

Early in my investigation of the behavior of the dancer I 
conceived the idea of determining the relation of modifiabihty 
of behavior (docility) to age. The question which was fore- 
most in my mind and for which I first sought an answer may 
be stated thus: can the dancer acquire a given habit with 
the same facility at different ages? Since the visual dis- 
crimination experiment seemed to be well suited for the 
investigation of this problem I planned to train, in the white- 
black discrimination experiment, five pairs of dancers at the 
age of one month, and the same number for each of the ages 
four, seven, ten, thirteen, sixteen, and nineteen months.^ 

* I have not been able thus far to determine the average length of the 
dancer's life. The greatest age to which any of my individuals has attained 
is nineteen months. 



Differe7ices in Behavior 271 

To test the same individuals month after month would be 
the ideal way of obtaining an answer to our question, but I 
could devise no satisfactory way of doing this. The effects 
of training last so long, as the results of the previous chapter 
proved, and the uncertainty of their entire disappearance is 
so serious, that the same training process cannot be used at 
successive ages. The use of different methods of training is 
even more unsatisfactory because it is extremely difficult 
to make accurate quantitative comparison of their results. 
It was these considerations that forced me to attempt to dis- 
cover the relation of docility to age by carrying out the same 
experiments with groups of individuals of different ages. 

As my plan involved the execution of precisely the same 
set of tests with at least seventy individuals whose age, his- 
tory, and past experience were accurately known, and of which 
some had to be kept for nineteen months before they could 
be trained, the amount of labor and the risk of mishap which 
it entailed were great. To make possible the completion 
of the investigation within two years, I accumulated healthy 
^ individuals for several months without training any of them. 
In March, 1907, I had succeeded in completing the tests for 
the age of one month, and I had on hand for the remaining 
tests almost a hundred individuals, whose ages ranged from 
a few days to eighteen months. Had everything gone well, 
the work would have been finished within six months. Sud- 
denly, and without discoverable external cause, my mice 
began to die of an intestinal trouble, and despite all my 
efforts to check the disease by changing food supply and en- 
vironment, all except a single pair died within a few weeks. 
Thus ended a number of experiments whose final results 
I had expected to be able to present in this volume. How- 
ever, the work which I have done is still of value, for the 
single pair of survivors have made possible the continuance 



272 



The Dancing Mouse 



of my tests with other individuals of the same Hne of de- 
scent as those which perished, and I have to regret only the 
loss of time and labor. 

As I have on hand results for ten individuals of the age of 
one month, and for four individuals of the age of four 
months, it has seemed desirable to state the problem, method, 
and incomplete results of this study of the relation of modi- 
fiability to age. The indices of modifiability for these two 
groups of dancers differ so strikingly that I feel justified in 

TABLE 52 
Plasticity (Relation of Modifiability to Age) 

Number of Errors in Successive Daily Series of Ten White-Black 
Tests, with Dancers Four Months Old 





Males 


Females 




Series 


















No. 76 


No. 78 


Av. 


No. 75 


No. 77 


Av. 


General Av. 


A 


7 


7 


7.0 


4 


8 


6.0 


6.50 


B 


8 


6 


7.0 


6 


5 


5-5 


6.25 


I 


5 


5 


5-0 


5 


5 


5-0 


5.00 


2 


5 


4 


4-5 


2 


2 


2.0 


3.25 


3 


4 


5 


4.5 


2 


5 


3-5 


4.00 


4 


3 


4 


3.5 


I 


I 


1.0 


2.25 


5 


5 


2 


3-5 





I 


0.5 


2.00 


6 


3 


2 


2-5 


I 





0-5 


1.50 


7 


2 


I 


1-5 


I 


2 


1-5 


1.50 


8 


5 


I 


3-0 











1.50 


9 


I 


3 


2.0 











I. GO 


10 


I 


2 


1-5 


I 





0-5 


I.OO 


II 


I 


I 


1,0 










0.50 


12 


I 


I 


I.O 










0.50 


13 






















14 




















15 





















Differences in Behavior 



^7Z 



persisting in my efforts to obtain comparable data for the 
seven ages which have been mentioned. 

The detailed results for the one-month old individuals 
appear in Table 43 ; those for the four-month individuals in 
Table 52. The general averages for the former are to be 
found in the third column of Table 46, under the heading 



150 



140 



120 
110 

































/ 

/ 










^^. /' ^ 






























/ 









































1 '4 7 10 13 

Figure 7,7,. — Plasticity curves. In the left margin are given the indices of 
modifiability (the number of tests necessary for the establishment of a perfect 
habit). Below the base line the age of the individuals is given in months. Curve 

for males, • — • — ; curve for females, ; curve for both males and 

females, — — . When these three plasticity curves are completed, they will repre- 
sent the indices of modifiability as determined for ten individuals at the age of 
I month, and similarly for the same number of individuals at each of the ages, 
4, 7, 10, 13, 16, and 19 months. 

*'io tests per day" ; those for the latter in the last column of 
Table 52. Mere inspection of these tables reveals the curious 
sex difference which goes far towards justifying the presenta- 
tion of this uncompleted work. The index of modifiabiUty 



2 74 The Dajtcing Mouse 

for the ten one-month individuals is 88 (that is, 88 tests were 
necessary for the estabhshment of a habit) ; for the four-month 
individuals it is 102.5. The heavy solid line of Figure 1^7^ 
joins the points on the ordinates at which these values are 
[located. Apparently, then, the dancer acquires the white- 
black discrimination habit less readily at the age of four 
months than at the age of one month. 

Further analysis of the results proves that this statement 
is not true. When the averages for the two sexes are com- 
pared, it appears that the males learned much less quickly 
at four months than at one month, whereas just the reverse 
is true of the females. The dash and dot line of the figure 
^extends from the index of modifiability of the one-month 
males (72) to that of the four-month males (120); and the 
regularly interrupted line similarly joins the indices of the 
one-month (104) and the four- month (85) females. In seek- 
ing to discover age differences in docility or ability to profit 
by experience we have stumbled upon what appears to be 
an important sex difference. Perhaps I should add to this 
presentation of partial results the following statement. Since 
there are only four individuals in the four-month group, two 
of each sex, the indices are not very reliable, and consequently 
too much stress should not be laid upon the age and sex differ- 
ences which are indicated. 

In view of this impressive instance of the way in which 
averages may conceal facts and lead the observer to false 
inferences, I wish to remark that my study of the dancer has 
convinced me of the profound truth of the statement that 
the biologist, whether he be psychologist, anthropologist, 
physiologist, or morphologist, should work with the organic 
individual and should first of all deal with his results as in- 
dividual results. Averages have their place and value, but 
to mass data before their individual significance has been 



Differences m Behavior 275 

carefully sought out is to conceal or distort their meaning. 
Too many of us, in our eagerness for quantitative results and 
in our desire to obtain averages which shall justify general 
statements, get the cart before the horse. 

Figure 33 presents the beginning of what I propose to call 
plasticity curves. When these three curves are completed 
on the basis of experiments with five dancers of each sex for 
each of the ages indicated on the base line of the figure, they 
will indicate what general changes in plasticity, modifiability of 
behavior, or abilit^to Jearn (for all of these expressions havd 
been used to designate much the same capacity of the organ^ 
ism) occur from the first month to the nineteenth in the male 
and the female dancer, and in the race without respect to sex. 
So far as I know, data for the construction of plasticity curves 
such as I hope in the near future to be able to present for the 
dancing mouse have not been obtained for any mammal. 

At present it would be hazardous for me to attempt to state 
any general conclusion concerning the relation of docility 
to age. 

The initiative of- the dancer certainly varies with its age. 
In scope the action system rapidly increases during the first 
few months of life, and if the animal be subjected to training 
tests, this increase may continue well into old age. The ap- 
pearance of noticeable quiescence does not necessarily indi- 
cate diminished initiative. Frequently my oldest mice have 
shown themselves preeminent in their ability to adjust their 
behavior to new conditions. However, I have not studied 
individuals of more than eighteen months in age. One would 
naturally expect initiative to decrease in senility. All that 
I can say is that I have seen no indications of it. 

We may now briefly consider the p rincipal sex difference s 
which have been revealed by the ex]:)eriments. In sensitive- 
ness I have discovered no difference, but it should be stated 



276 The Dancing Mouse 

that no special attention has been given to the ma.tter. In 
docility the males usually appeared to be superior to the 
females. This was especially noticeable early in my visual 
discrimination tests. The males almost invariably acquired 
a perfect habit quicker than the females. I may cite the 
following typical instances. Number 14 acquired the black- 
white habit with 40 tests; No. 13, with 60 (Table 10, p. 109). 
Of the five pairs of individuals whose records in white-black 
training appear in Table 43, not one contradicts the statement 
which has just been made. It is to be noted, however, that 
under certain conditions of training, for example, 20 tests per 
day, the female is at an advantage. Recently I have with 
increasing frequency obtained measures of docility which 
apparently favor the female. That this difference in the 
results is due to a difference in age is probable. 

In labyri nth te sts the f emal e is as mjuch superior \q the 
male as the male is to the female in discrimination tests. 
From the tables of Chapter XIII I may take a few averages 
to indicate the quantitative nature of this difference. A de- 
gree of proficiency in labyrinth B attained by the males after 
7.0 trials was equaled by the females after 6.2 trials. In 
labyrinth C the males acquired a habit as a result of 18.7 
trials ; the females, as a result of 13.8. And similarly in laby- 
rinth D, 6.1 trials did no more for the males than 5.9 did for 
the females. 

That at the age of about one month the male dancer should 
be able to acquire a visual discrimination habit more rapidly 
than the female, whereas the female can acquire a labyrinth 
habit more readily than the male, suggests an important 
difference in the nature of their equipment for habit forma- 
tion. || One might hazard the suggestion that the male de- 
pends more largely upon discrimination of external condi- 
tions, whereas the female depends to a greater extent than 



Differences in Behavior 277 

does the male upon the internal, organic changes which are 
wrought by acts. At any rate the female seems to follow a 
labyrinth path more mechanically, more accurately, more 
easily, and with less evidence of sense discrimination than 
does the male. 

Finally, in concluding this chapter, I may add that in those 
aspects of behavior which received attention in the early 
chapters of this volume the dancers differ very markedly. 
Some climb readily on vertical or inclined surfaces to which 
they can cling ; others seldom venture from their horizontally 
placed dance floor. Some balance themselves skillfully on 
narrow bridges; others fall off almost immediately. My 
own observations, as well as a comparison of the accounts 
of the behavior of the dancer which have been given by Cyon, 
Zoth, and other investigators, lead me to conclude that there 
are different kinds of dancing mice. This may be the result 
of crosses with other species of mice, or it may be merely an 
expression of the variability of an exceptionally unstable 
race. 

I can see no satisfactory grounds for considering the dancer 
either abnormal or pathological. It is a well-established 
race, with certain peculiarities to which it breeds true; and 
no pathological structural conditions, so far as I have been 
able to learn, have been discovered. 

I have presented in this chapter on differences a program 
rather than a completed study. To carry out fully the lines 
of work which have been suggested by my observations and 
by the presentation of results would occupy a skilled observer 
many months. I have not as yet succeeded in accomplishing 
this, but my failure is not due to lack of interest or of effort. 



CHAPTER XVIII 

The Inheritance of Forms of Behavior 

1 In a general way those peculiarities of behavior which 
[suggested the name dancing mouse are inherite d. Genera- 
tion after generation of the mice run in circles, whirl, and 
move the head restlessly and jerkily from side to side. But 
these forms of behavior vary greatly. Some individuals 
whirl infrequently and sporadically ; others whirl frequently 
and persistently, at certain hours of the day. Some are 
unable to climb a vertical surface ; others do so readily. Some 
respond to sounds; others give no indications of ability to 
hear. I propose in this chapter to present certain facts con- 
cerning the inheritance of individual peculiarities of behavior, 
and to state the results of a series of experiments by which I 
had hoped to test the inheritance of individually acquired 
forms of behavior. 
I My study of the nature of the whirling tendency of the 
dancer has revealed the fact that ce rtain individu als whirl to 
the right almost juniformly, others just as regularly to the 
left, and still others now in one direction, now in the other. 
On the basis of this observation, the animals have been classi- 
fied as right, left, or mixed whirlers. Does the dancer 
transmit to" its offspring the tendency to whirl in a definite 
manner ? 

Records of the direction of whirling of one hundred in- 
dividuals have been obtained. For twenty of these mice 
the determination was made by counting the number of com- 

278 



The Inheritance of Forms of Behavior 279 

plete turns in five-minute intervals at six different hours of 
the day. For the remaining eighty individuals the direction 
was discovered by observation of the activity of the animals 
for a brief interval at five different times. Naturally, the 
former results are the more exact ; in fact, they alone have 
any considerable quantitative value. But for the problem 
under consideration all of the determinations are sufficiently 
accurate to be satisfactory. 

The distribution of the individuals v^hich were examined as 
to direction of whirling is as follows. 



Right Whirlers 


Left Whirlers 


Mixed Whirlers 


TOTA 


Males 19 


19 


12 


50 


Females 12 


23 


15 


SO 



The frequency of occurrence of left whirlers among the 
females is unexpectedly high. Is this to be accounted for 
in terms of inheritance ? In my search for an answer to this 
question I followed the whirling tendency from generation 
to generation in two lines of descent. These two groups of 
mice have already been referred to as the 200 line and the 
400 line. The former were descended from Nos. 200 and 
205, and the latter from Nos. 152 and 151. Individuals 
which resulted from the crossing of these lines will.be referred 
to hereafter as of mixed descent. There were some striking 
differences in the behavior of the mice of the two lines of 
descent. As a rule the individuals of the 200 line climbed 
more readily, were more active, danced less vigorously, 
whirled less rapidly and less persistently, and were in several 
other respects much more like common mice than were the 
individuals of the 400 line. It is also to be noted (see Table 
5, p. 89) that few of the litters of the 200 line exhibited 
auditory reactions, whereas almost all of the litters of the 
400 line which were tested gave unmistakable evidence of 



28o The Da7icing Mouse 

sensitiveness to certain sounds. These differences at once 
suggest the importance of an examination of the whirling 
tendency of each Hne of descent. 

The results for the several generations of each line which 
I had opportunity to examine are unexpectedly decisive so 
far as the question in point is concerned. 

Individuals of the 200 Line 

Males Females 

First generation No. 200, ? No. 205, ? 

Second generation No. 210, Mixed whirler No. 215, Left whirler 

Third generation No. 220, Mixed whirler No. 225, Mixed whirler 

Fourth generation No. 230, Right whirler' No. 235, Mixed whirler 

Fifth generation No. 240, Right whirler No. 245, Left whirler 

Individuals of the 400 Line 

Males Females 

First generation No. 152, Left whirler No. 151, Left whirler 

Second generation No. 410, Left whirler No. 415, Right whirler 

Third generation No. 420, Left whirler No. 425, Left whirler 

One line of descent exhibited no pronounced whirling 
tendency; the other exhibited a strong tendency to whirl to 
the left. Are these statements true for the group of one hun- 
dred individuals whose distribution among the three classes 
of whirlers has been given? In order to obtain an answer 
to this question I have reclassified these individuals accord- 
ing to descent and direction of whirling. 

Individuals of the 200 Line 



Right Whirlers 


Left Whirlers 


Mixed Whirlers 


TOT^ 


Males 7 


6 


8 


21 


Females j^ 


_8 


8 


2£ 


12 


14 


16 


42 



The Inheritance of Forms of Behavior 281 
Individuals of the 400 Line 

Right Whirlers Left Whirlers Mixed Whirlers Total 



Males 


4 


9 


I 


14 


Females 


_6 


3. 


£ 


IS 




10 


18 


5 


Z2, 



Individuals of Mixed Descent 
9 10 6 25 

Three interesting facts are indicated by these results: 
first, the inheritance of a tendency to whirl to the left in the 
400 line of descent ; second, the lack of any definite whirling 
tendency in the 200 line; and third, the occurrence of right 
and left whirlers with equal frequency as a result of the cross- 
ing of these two lines of descent. 

It is quite possible, and I am incHned to consider it prob- 
able, that the pure dancer regularly inherits a tendency to 
whirl to the left, and that this is obscured in the case of the 
200 line by the influences of a cross with another variety of 
mouse. It is to be noted that the individuals of the 200 line 
were predominantly mixed whirlers, and I may add that 
many of them whirled so seldom that they might more appro- 
priately be classed as circlers. 

The Inheritance of Individually Acquired Forms of 

Behavior 

The white-black discrimination experiments which were 
made in connection with the study of vision and the modi- 
fiability of behavior were so planned that they should furnish 
evidence of any possible tendency towards the inheritance 
of modifications in behavior. The problem may be stated 
thus. If a dancing mouse be thoroughly trained to avoid 
black, by being subjected to a disagreeable experience evety 



282 



The Dancing Mouse 



time it enters a black box, will it transmit to its offspring a 
tendency to avoid black? 

Systematic training experiments were carried on with 
individuals of both the 200 and 400 lines of descent. For 
each of these lines a male and a female were trained at the 
age of four weeks to discriminate between the white and the 
black electric-boxes and to choose the former. After they 
had been thoroughly trained these individuals were mated, 

TABLE 53 

The Inheritance of the Habit of White-Black Discrimination 

Number of Errors in Daily Series of Ten Tests 





Males 


Females 


Series 


First 


Second 


Third 


Fourth 


First 


Second 


Third 


Fourth 




Fenera- 


Genera- 


Genera- 


Genera- 


Genera- 


Genera- 


Genera- 


Genera- 




tion 


tion 


tion 


tion 


tion 


tion 


tion 


tion 




No. 210 


No. 220 


No. 230 


No. 240 


No. 215 


No. 225 


No. 235 


No. 24s 


A 


6 


5 


6 


7 


8 


4 


4 


7 


B 


6 


8 


8 


8 


8 


7 


6 


5 


I 


6 


7 


6 


5 


7 


6 


5 


4 


2 


4 


3 


I 


5 


5 


6 


4 


5 


3 


3 


I 


4 


5 


3 


4 


4 


3 


4 


5 





3 


4 


2 


I 


3 


I 


5 


3 





4 


2 


I 


3 


3 





6 


2 


I 


4 


2 


2 


I 


I 


I 


7 


I 





3 


I 


I 


I 


2 





8 








I 











2 


3 


9 











I 


I 











10 










I 





2 


I 


I 


II 















3 








12 























13 






















14 

























The Inheritance of Forms of Behavior 283 

and in course of time a male and female, chosen at random 
from their first litter, were similarly trained. All the individ- 
uals were trained in the same way and under as nearly the 
same conditions as could be maintained, and accurate records 
were kept of the behavior of each animal and of the number 
of errors of choice which it made in series after series of tests. 
What do these records indicate concerning the influence 
individually acquired forms of behavior upon the behavior 
of the race ? 

I have records for four generations in the 200 line and for 
three generations in the 400 line.* As the results are prac- 
tically the same for each, I shall present the detailed records 
for the former group alone. In Table 53 are to be found the 
number of errors made in successive series of ten tests each 
by the various individuals of the 200 line which were trained 
in this experiment. The most careful examination fails to 
reveal any indication of the inheritance of a tendency to avoid 
the black box. No. 240, in fact, chose the black box more 
frequently in the preference series than did No. 210, and he 
required thirty more tests for the establishment of a perfect 
habit than did No. 210. Apparently descent from individuals 
which had thoroughly learned to avoid the black box gives 
the dancer no advantage in the formation of a white-black 
discrimination habit. There is absolutely no evidence of 
the inheritance of this particular individually acquired form 
of behavior in the dancer. 

^ This experiment was interrupted by the death of the animals of both 
lines of descent. 



INDEX 



Abnormal dancers, 277. 

Acquired forms of behavior, 281. 

Act, useless, repeated, 106, 205. 

Activity, periods of, 34. 

Affirmation, choice by, 131. 

Age, pecuUarities, 264, 269; maxi- 
mum age, 270; and intelligence, 
272. 

Albino cat, 65; dog, 32. 

Alexander and Kreidi, young dancer, 
21, 23; behavior, 30, 42; tracks 
of mice, 44; behavior in cyclostat, 
46; behavior of w^hite mouse and 
dancer, 48 ; structure of ear, 58-65 ; 
deafness, 76. 

Allen, G. M., drawing of dancer, 3; 
heredity in mice, 11. 

Alleys, width of, in labyrinths, 214. 

Amyl acetate for photometry, 121. 

Anatomy of dancer, 52. 

Animals, education of, 200. 

Appuun whistles, 79. 

Audition. See Hearing. 

Averages, dangers in, 274. 

Baginsky, B., model of ear of dancer, 

58, 59, 63, 67. 
Bateson, W., breeding experiments, 

i3> 14. 
Behavior, of dancer, 5, 29; inherit- 
ance of, 37, 278; when blinded, 
42, 47; equilibration, 42; dizzi- 
ness, 45; structural bases of, 52; 
of young, 22; changes in, 21, 85; 
useless acts, 106, 205; under ex- 
perimental conditions, 129; in in- 
discriminable conditions, 132; value 
of sight, 178; in labyrinth experi- 
ments, 188; modifiability of, 199; 
history of, 206; explanations of, 
206; individual differences in, 
264, 277. 



Blinded dancers, behavior of, 42, 47. 
Blue-orange tests, 140; blue-red tests, 

145, 173; blue-green tests, 170; 

blue-green blindness, 172. 
Bradley papers, 133, 140. 
Brain, structure of, 29, 69, 71. 
Breeding of dancers, i, 13, 20. 
Brehm, A. E., "Tierleben," i, 8. 
Brightness vision, 91; preference, 

105; check experiments, 140; 

relation to color vision, 177. 

Cages for dancfers, 16. 

Candle meter, 156. 

Candle power, 121. 

Cardboards, for tests of vision, 95; 
positions of, iii. 

Care of dancer, 18. 

Castle, W. E., drawing of mouse, 3; 
cages, 16. 

Cat, albino, 65 ; training of, 200, 228. 

Cerebellum of dancer, 72. 

Characters, acquired, 281. 

Check experiments, 140. 

China, dancers of, 5, 14. 

Choice, exhibition of, 96; by affir- 
mation, 131; by negation, 131; 
by comparison, 131; methods of, 
200, 234. 

Circling, a form of dance, 32. 

Circus course mice, 2. 

Cleghorn, A. G., 2. 

Climbing of dancer, 42, 269, 277. 

Cochlea, functions of, 61. 

Color blindness, 169. 

Color discrimination apparatus, 134, 

151- 
Colored glasses, 151, 155. 
Colored papers, 133, 139, 140. 
Color patterns of dancers, i, 4. 
Color vision, problem, 91, 177; 

methods of testing, 133, 137, 151; 



28s 



286 



Index 



tests with colored papers, 133-150; 
tests with ray filters, 151-177; 
orange-blue tests, 138; yellow-red 
tests, 139; light blue-orange tests, 
140; dark blue-red tests, 145; 
green-hght blue tests, 147; violet- 
red tests, 148; green-blue tests, 
158; green-red tests, 163; blue- 
green tests, 170; blue-red tests, 
173; structure of the retina, 177; 
conclusions, 176; of different ani- 
mals, 143. 

Comparative pedagogy, 239. 

Comparison, choice by, 131. 

Cones, lacking in eye of dancer, 177. 

Corti, organ of, in dancer, 54, 65. 

Cotton mouse, 8. 

Curves, of habit formation, 217, 231, 
233, 235, 273; irregularities of , 232; 
of labyrinth habit, 236; of dis- 
crimination habit, 236; of learning 
and re-learning, 257; of plasticity, 

273- 

Cyclostat, behavior of dancer in, 46. 

Cyon, E. de, dancer pathological, 
11; behavior, 30, 41; behavior of 
blinded dancers, 47; varieties of 
dancer, 48-50, 56; space percep- 
tion, 63, 67; individual differences, 
69; anatomy of dancer, 70; hear- 
ing of dancer, 74-81 ; pain cries, 75. 

Dancers, occurrence among com- 
mon mice, 9; varieties of, 49, 277; 
hybrid, 13. 

Dancing, 2, 5 ; forms of dance move- 
ment, 32; whirling, circHng, figure- 
eights, manege movements, solo 
dance, contre dance, 32-33; direc- 
tion of, 2)T^^ 281; periods of, 34, 39; 
amount of, 39; causes of, 31, 70; 
sex differences in, 34; individual 
differences in, 277, 278. 

Darbishire, A. D., breeding experi- 
ments with dancers, 13. 

Deafness of dancer, 53, 61, 73 ; causes 
of, 68, 71, 72. 



Descent, lines of, 90, 279. 
Development of young dancer, 22-28. 
Differences, individual, 50, 197, 199, 

215, 221, 234, 254, 264; age, 269, 

270; sex, 199, 221, 274. 
Direction of movement, choice by, 

109. 
Direction of whirling, -^Z^ 281. 
Discrimination, visual, box, 92; of 

brightness, 95, 132; white-black 

and black- white, 103-109; of 

grays, 115; habits, 147; by odor, 

149; by form, 179; method, 227; 

habit defined, 147, 231. 
Diseases of dancer, 16, 241, 271. 
Dizziness, 42, 44-47, 63; visual, 45, 

46; rotational, 46. 
Docility, 200, 264, 270. 
Dog, albino, 32; training of, 228; 

fear of electric shock, 225. 

Ear, structure of, 53-71; structural 
types, 56; model of, 58; of rabbit, 
54; functions of, 61, 62-72; move- 
ments of, 77. . 

Educability of dancer, 126, 199. 

Education, human, 199; methods 
of, 239; of vision, 126. 

Efficiency of training, 239. 

Electric-box for visual tests, 92. 

Electric-labyrinth for habit experi- 
ments, 187. 

Electric-shock as punishment for 
mistakes, 82, 94, 100. 

Epidemic among dancers, 241, 271. 

Equilibration in dancer, 41-44, 62. 

Error curves, 231, 235; form of , 232. 

Error records versus time records, 
217. 

Errors, in labyrinths, 184, 210, 211, 
222; nature of, 223; types of, 222- 
225 ; value of, 225 ; number of, 223. 

Even numbers to designate males, 3, 
102. 

Excitability of dancer, 31, 85. 

Experience, value of, 199; infliience 
of, 262, 263. 



Index 



287 



Eyes, of dancer, 3; opening of, 24; 
retina of, 177. 

Fear, in dancer, 45. 

Females, designated by odd num- 
bers, 3, 102; dancing of, 34, 36; 
voice of, 75. See Sex. 

Fighting of dancers, 20. 

Figure-eight dance, 32. 

Filters for obtaining colored light, 

151-155- 
Food of dancer, 19, 20. 
Form discrimination, 179, 182. 
Frog, reactions of, 81; repetition of 

act by, 205. 
Functions of eye, 177. 

Galton whistle, 74, 76. 
Gestation, period of, in dancer, 21. 
Gray papers, 113. 
Green-blue tests, 147, 158. 
Green-red tests, 163. 
Grouping for averages, 237. 
Guaita, G. von, breeding experi- 
ments with dancers, 13, 14. 

Haacke, W., description of dancer, 
i; origin of dancer, 8; breeding 
experiments, 13. 

Habit, of dancing, 40; discrimina- 
tion, 147; useless, 106, 205; laby- 
rinth, 210; duration of, 251; 
reacquisition of, 256; relations of, 
262. 

Habit formation, and the senses, 196; 
versus habit performance, 197; in 
the dancer and in the common 
mouse, 212; curves of, 217, 231, 
235; speed of, 234. 

Habituation to sounds, 90. 

Hacker, dancing shrews, 11. 

Hair, appearance of, 22. 

Hamilton, G. V., experiments with 
dog, 225. 

Hatai, S., the dancer, 7, 8. 

Head, shape of, in dancer, 2, 49. 

Hearing, in dancer, 62, 73; in young 



78; in adult, 90; methods of test- 
ing, 79; in frog, 81. • 

Hefner unit of light, 121. 

Heredity, 90, 278. See Inheritance. 

Hering, E., colored papers, 139. 

History, of dancer, i ; of acts, 206. 

Hunger as motive in experiments, 98. 

Hybrid dancers, 13. 

# 

Imitation in dancer, 206-209. 

Index of modifiability, 237, 248, 261, 
272. 

Individuality, 49, 61, 197, 199, 206, 
215, 221, 234, 254, 264, 277. 

Inheritance, 9, 13, 37, 68, 90, 278. 

Inhibition of an act, 130. 

Initiative of dancer, 200, 264, 268. 

Insight of dancer, 234. 

Intelligence, 206; measures of, 210, 
227; comparisons, 234. 

Interrupted circuit for experimental 
use, 94. 

Irregular labyrinths, 222. 

J ANSSEN- Hoffman spectroscope, 155. 
Japan, dancers in, 5, 7. 
Judgment in dancer, 131. 

Kammerer, p., dancing wood mice, 

10. 
Kishi, K., dancer in Japan, 5; origin 

of race, 9; equilibration, 45; 

blinded dancer, 48; structure of 

ear, 59, 63, 64-69; wax in ears, 74; 

tests of hearing, 77. 
Konig tuning forks, 84 ; steel bars, 87 . 
Kreidl, A. See Alexander. 

Labyrinth, forms of, 210; labyrinth 
A, 211, errors in, 211, tests in, 213; 
labyrinth B, 184, tests, 216; laby- 
rinth C, 219, 221; labyrinth D, 
222, 224; a standard labyrinth, 
224; regular and irregular laby- 
rinths, 222. 

Labyrinth errors and individual ten- 
dencies, 225. 



288 



Index 



Labyrinth habits, 262. 
Labyrinth method, 200, 225. 
Labyrinth path, formula, 222, 225; 

method of recording, 219. 
Ladder dimbing tests, 201. 
Landois, H., account of dancer, 2. 
Lathrop, A., dancers, 11. 
Learning, process, 239; methods of, 

in dancer, 199; by being put 

through act, 201; by imitation, 

206; by rote, 234; rapidity of, 

227, 234, 239; permanency of , 239; 

learning and re-learning, 25 1 ; 

curves of, 257. 
Left whirlers, 37, 225, 279. 
Life span of dancer', 228, 270. 
Light, reflected, 151; transmitted, 

151; unit of measurement, 121; 

control of, 156. 
Litter, size of, in dancer, 21, 23. 
Lummer-Brodhun photometer, 121, 

157- 

Males, dancing of, 34; fighting and 
killing young, 20; designation of, 
3,102; voice of, 75. 5ee Sex. 

Manege movements, 32. 

Mark, E. L., cages, 16. 

Maze. See Labyrinth. 

Measurements, of light, 121, 156; of 
rapidity of habit formation, 210, 
227; of intelligence, 237; of effi- 
ciency of training, 239. 

Memory, defined, 251; for ladder 
climbing, 205; tests of, 252; 
measurements of, 254; span of, 
254; for brightness, 255; for 
color, 256. 

Method, of studying dance, T^y, for 
testing hearing, 79; indirect, 81; 
for testing vision, 92; motives, 98; 
for brightness vision, 92, 113; for 
color vision, 133, 151; of shifting 
filters, 152; of testing form dis- 
crimination, 179, 182; of testing 
Weber's law, 1 18-129; develop- 
ment of methods, 145, 210, 233; 



of choice, 131; food-box, 134; 
labyrinth, 184; of recording er- 
rors, 189, 191, 220; of training: 
problem method, labyrinth method, 
discrimination method, 199; of 
recording labyrinth path, 219; 
qualitative -yer^M^ quantitative, 226, 
227; of studying senses, 226; val- 
ues of methods, 227; of measuring 
intelligence, 227; quantitative, 238; 
comparisons of, 246. 

Milne-Edwards, origin of dancer, 1 2, 
14. 

Mitsukuri, K., the dancer in Japan, 
7,8. 

Mixed whirlers, 34, 279. 

Modifiability, of behavior, 199; of 
useless acts, 205; index of, 237, 
248, 261, 272. 

Motives, for activity, 82, 98; for 
choice, 137; avoidance of dis- 
comfort, 188; in labyrinths, 212, 
218; desire to escape, to get food, 
to avoid pain, 225. 

Motor, tendencies, 178; ability, 214; 
capacity, 228. 

Movements, 2, 5, 32; of ears, 77. 

Mus musculus L., 7, 12, 15. 

Mus spiciosus L., 7. 

Mus sylvaticus L., 10. 

Nankin nesumi, name for dancer, 5, 

7- 
Negation, choice by, 131. 
Nendel, R., gray papers, 114. 
Nerve, eighth, 60. 
Nervous system, 69, 71, 72. 
Nest materials, 18. 
Noises, effects of, 79. 
Numbers, odd for females, even for 

males, 3, 102; reference, i. See 

Bibliographic List, xix. 

Odors, discrimination by, loi, 149. 
Old Fancier's description of dancer, 

29. 
Olfactory sense. See Smell. 



Index 



289 



Orange-blue tests, 138. 

Orientation of dancer, 47, 49, 62. 

Origin of dancer, i, 5, 8-15; by 
selectional breeding, 8, 12; by 
inheritance of an acquired char- 
acter, 9, 68; by mutation, 9; by 
pathological changes, 11; by natu- 
ral selection, 12. 

Panse, R., structure of ear, 55-59, 
63 ; explanation of deafness, 67, 73. 

Papers, Nendel's grays, 114; Brad- 
ley's colored, 133, 140; Hering's 
colored, 139. 

Parker, G. H., structure of retina, 177. 

Path in labyrinth, record of, 219, 220. 

Pathological condition of dancer, 11, 
277. 

Pedagogy, comparative, 239. 

Perception, of brightness, 91-132; of 
color, 133-177; of movement, 179; 
of form, 179, 182. 

Peru, dancers in, 8. 

Petromyzon, semicircular canals of, 

63- 
Photometer, Lummer-Brodhun, 121, 

157- 
Plasticity, of dancer, 272; curves of, 

273- 
Position, choice by, loi, 109, 229; 

of cardboards, in. 
Preference for brightness, 105, 232, 

257; tests of, 104, 105. 
Preliminary tests, 215, 229. 
Probable error, 237. 
Problems, of structure, 72; of 

method, 200, 226. 
Punishment versus reward, 98, 99, 

188. 
Putting-through, training by, 201. 

Qualitative methods, 226, 227. 
Quantitative methods, 226, 227, 238. 

Rabbit, ear of, 54, 55. 
Rawitz, B., behavior of dancer, 30, 
31; structure of ear, 53-58, 66, 67, 



68, 69; deafness of dancer, 73; 

hearing in young, 78, 84. 
Ray filters, 152. 

Reactions, to sounds, 73-90; to dis- 
agreeable stimuli, 100; valueless, 

106, 205. 
Reasoning, implicit, 131, 234. 
Reconstruction method, 53, 58. 
Records, of markings of dancers, 3, 

4; of time, 216, 217; of errors, 217; 

of path, 220. 
Red, stimulating value of, 146, 165, 

169, 175; vision, 139, 145, 148, 

163, 173- 
Reference numbers to literature, i. 

See Literature on Dancer, xix. 
Reflected light, 112. 
Refrangibility and vision of dancer, 

165. 
Regular labyrinth, 222. 
Re -learning, relation to learning, 25 1 ; 

curves of, 257. 
Reliability of averages, 236, 237. 
Repetition of useless acts, 106, 205. 
Rest-interval, definition of, 252, 
Restlessness, of dancer, 30, 31, 77; 

cause of, 31. 
Retina of dancer, 177. 
Retzius, ear of rabbit, 54. 
Reward, for performance of act, 98; 

versus punishment, 99, 137. 
Right whirlers, 34, 37; behavior in 

labyrinth, 220; occurrence of, 279; 

inheritance of tendency, 279. 
Rods of retina, 177. 
Rotational dizziness, 47. 
Rubber stamps of labyrinths, 219, 220. 

Saint-Loup, R., origin of dancer, 9, 

10, 14. 
Schlumberger, C, origin of dancer, 

12; wood carving with dancers, 12. 
Selenka, ear of rabbit, 54. 
Semicircular canals, 53-72. 
Sense organs, 23, 26, 27. 
Senses, and habit formation, 196, 

226; differences in, 265. 



290 



Lidex 



Sensitiveness, 264. 

Sex, recognition of, 21; designation 

of, 3, 102; peculiarities, 199, 221, 

261, 264, 274. 
Shellac to coat cards, ici, 149. 
Shrews, dancing, 10. 
Sight, role of, 178. See Vision, 

Brightness Vision, and Color Vision. 
Smell, sense of, 31, loi; in labyrinth 

habits, 189, 196, 
Sniffing by dancer, 31. 
Solutions as ray filters, 154, 155. 
Sorex vulgaris L., 10. 
Sound, reactions to, 79. 
Space perception, 63, 67, 71. 
Spectroscope, 155. 
Spectrum, stimulating value of, 139, 

146, 165, 169, 175. 
Standard, candle, 121; light, 120, 

126; labyrinth, 224. 
Stine, W. M., photometrical measure- 
ments, 121. 
Strength of dancer, 3. 
Structure, 52-72; of brain, 69, 71; 

of ear, 52-72; of eye, 177. 
Swinhoe, mice in China, 7. 

Temperament of animal, 228. 

Temperature sense, 20, 80. 

Tests, visual, 91-198; number of, 
per day, 148, 249. 

Threshold of discrimination, 116, 123. 

Time records, 204, 216. 

Touch, 178; and labyrinth habits, 
190, 194, 195. 

Training, conditions of, 107 ; Weber's 
law, 118, 126; methods of, 199; 
and retraining, 256; in labyrinths, 
210; efficiency of, 239; two-test, 
240; ten-test, 243; twenty-test, 



244; continuous, 245; relation to 
methods, 261; spread of, 262. 
Transmitted light, 112. 

Variability of dancer, 11, 48, 49, 
277. 

Variable light, 120. 

Varieties of dancer, 49, 89. 

Violet-red tests, 148. 

Vision, 42, 47, 48, 91; brightness 
vision, 91-132; color vision, 133- 
177; training of, 126; importance 
of, 178; conclusions concerning 
198. 

Visual dizziness, 45. 

Voice of dancer, 75, 76. 

Watson, J. B., habit formation, 198. 

Waugh, K., color-vision apparatus, 
135; retina of mouse, 177. 

Wax, plugs of, in ear of mouse, 68, 74. 

Weber's law tests of, 113; apparatus, 
118. 

Weldon, W. F. R., breeding experi- 
ments, xxi. 

Whirling of dancer, 32, 34. 

Yellow-red tests, 139. 

Young dancers, killing of, by male, 
20; description of, 22; develop- 
ment of, 24; hearing of, 85; in- 
telligence of, 274; size of, 23. 

Zoth, O., origin of dancer, 14; size 
of young mice, 23; the senses of 
dancer, 31; behavior, 32; dancing, 
39; equilibration, 41; climbing 
dancers, 43, 49; individual dif- 
ferences, 69; tests of hearing, 77; 
vision, 91. 



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